macaca-cli: xctest client proxy error with: Error: connect ECONNREFUSED 172.18.156.69:8100

os: os x 10.11.6 macaca version:1.1.2 ios driver: 1.0.36 device: iPhone6S(9.3.5) 真机运行时，大概率会反复出现此错误(同样的代码步骤可以正常运行过)。出现此提示失败后，设备上过了一段时间才会自动启动起WebDriverAgent并自动关闭。

ERROR LOG:

QA-deMac-mini:~ qa$ macaca server --verbose
>> index.js:17:12 [master] pid:6048 webdriver server start with config:
 { port: 3456,
  verbose: true,
  ip: '192.168.241.195',
  host: 'QA-deMac-mini.local',
  loaded_time: '2016-09-12 18:15:55' }
>> middlewares.js:17:10 [master] pid:6048 base middlewares attached
>> router.js:108:10 [master] pid:6048 router set
>> webdriver sdk launched
>> responseHandler.js:11:12 [master] pid:6048 Recieve HTTP Request from Client: method: POST url: /wd/hub/session, jsonBody: {"desiredCapabilities":{"platformVerison":"9.3.5","platformName":"iOS","bundleId":"com.nd.app.factory.jianggongyouth","udid":"<udid>","browserName":"firefox","version":"","javascriptEnabled":true,"platform":"ANY"}}
>> session.js:47:10 [master] pid:6048 Creating session, sessionId: e9d76ab1-ae08-4d74-890b-0f4f5f1dddda.
>> xctest-client.js:43:14 [master] pid:6048 project path: /usr/local/lib/node_modules/macaca-ios/node_modules/xctest-client/node_modules/webdriveragent/WebDriverAgent/WebDriverAgent.xcodeproj
>> macaca-ios.js:130:10 [master] pid:6048 {
    "bundleId": "com.nd.app.factory.jianggongyouth",
    "platformName": "iOS",
    "browserName": "firefox"
}
>> xctest-client.js:183:12 [master] pid:6048 xcode version: 7.3.1
>> WebDriverAgent version: 1.0.25
>> xctest-client.js:156:14 [master] pid:6048 2016-09-12 18:16:03.293 xcodebuild[6054:27353] [MT] IDETestOperationsObserverDebug: (87020BAC-33C0-4DE0-BB81-50C355B6773B) Beginning test session 87020BAC-33C0-4DE0-BB81-50C355B6773B with Xcode 7D1014 on target <DVTiOSDevice: 0x7f85c5683720> {
        deviceSerialNumber:         FK1QF2JTGRYC
        identifier:                 <udid>
        deviceClass:                iPhone
        deviceName:                 My iPhone
        deviceIdentifier:           <udid>
        productVersion:             9.3.5
        buildVersion:               13G36
        deviceSoftwareVersion:      9.3.5 (13G36)
        deviceArchitecture:         arm64
        deviceTotalCapacity:        59669319680
        deviceAvailableCapacity:    7193366528
        deviceIsTransient:          NO
        ignored:                    NO
        deviceIsBusy:               NO
        deviceIsActivated:          YES
        deviceActivationState:      Activated
        deviceType:                 <DVTDeviceType:0x7f85c53c0a90 Xcode.DeviceType.iPhone>
        supportedDeviceFamilies:    (
    1
)
        applications:              (null)
        provisioningProfiles:      (null)
        activityProgress:          -2
        activityTitle:             
        hasInternalSupport:        NO
        isSupportedOS:             YES
        developerDiskMountError:   (null)
(null)
    } (9.3.5 (13G36))

>> xctest-client.js:156:14 [master] pid:6048 2016-09-12 18:16:03.296 xcodebuild[6054:27355]  IDETestOperationsObserverDebug: Writing diagnostic log for test session to:
/Users/qa/Library/Developer/Xcode/DerivedData/WebDriverAgent-drmzhetqodgefhaqpyureuezairh/Logs/Test/616A811A-9156-45F8-A4E1-969BE3F2DAD9/Session-2016-09-12_18:16:03-bizmtg.log

>> xctest-client.js:156:14 [master] pid:6048 MDMCreateDeltaDirectory:1920 calling MDMDirectoryDiff with:
state->old_bundle: /var/folders/7x/rvnhm1zs44j1mkq4fg6qzqqm0000gn/C/com.apple.DeveloperTools/All/Xcode/EmbeddedAppDeltas/7566f7ff6f0cd873d892945ee2a11b48/<udid>/WebDriverAgentRunner-Runner.app
state->new_bundle: /Users/qa/Library/Developer/Xcode/DerivedData/WebDriverAgent-drmzhetqodgefhaqpyureuezairh/Build/Products/Debug-iphoneos/WebDriverAgentRunner-Runner.app
state->dst_bundle: /var/folders/7x/rvnhm1zs44j1mkq4fg6qzqqm0000gn/C/com.apple.DeveloperTools/All/Xcode/EmbeddedAppDeltas/WebDriverAgentRunner-Runner.app.BC8Qop/WebDriverAgentRunner-Runner.app_sparse.ipa/Payload//WebDriverAgentRunner-Runner.app, binaryDiff flag: FALSE
    dst_ipa: /var/folders/7x/rvnhm1zs44j1mkq4fg6qzqqm0000gn/C/com.apple.DeveloperTools/All/Xcode/EmbeddedAppDeltas/WebDriverAgentRunner-Runner.app.BC8Qop/WebDriverAgentRunner-Runner.app_sparse.ipa

>> xctest-client.js:156:14 [master] pid:6048 __MDMDirectoryDiff_block_invoke37:1473 calling writeDictToFile with: /var/folders/7x/rvnhm1zs44j1mkq4fg6qzqqm0000gn/C/com.apple.DeveloperTools/All/Xcode/EmbeddedAppDeltas/WebDriverAgentRunner-Runner.app.BC8Qop/WebDriverAgentRunner-Runner.app_sparse.ipa/ManifestCache.plist

>> xctest-client.js:156:14 [master] pid:6048 writeDictToFile:1278 ==== Successfully wrote Manifest cache to /var/folders/7x/rvnhm1zs44j1mkq4fg6qzqqm0000gn/C/com.apple.DeveloperTools/All/Xcode/EmbeddedAppDeltas/WebDriverAgentRunner-Runner.app.BC8Qop/WebDriverAgentRunner-Runner.app_sparse.ipa/ManifestCache.plist

>> proxy.js:54:14 [master] pid:6048 Proxy: /session:POST to http://172.18.156.69:8100/session:POST with body: {"desiredCapabilities":{"bundleId":"com.nd.app.factory.jianggongyouth","platformName":"iOS","browserName":"firefox"}}
>> proxy.js:58:18 [master] pid:6048 xctest client proxy error with: Error: connect ECONNREFUSED 172.18.156.69:8100
/usr/local/lib/node_modules/macaca-ios/node_modules/xlogger/lib/xlogger.js:169
  throw new Error(res);
  ^

Error: >> proxy.js:58:18 [master] pid:6048 xctest client proxy error with: Error: connect ECONNREFUSED 172.18.156.69:8100
    at Logger.error (/usr/local/lib/node_modules/macaca-ios/node_modules/xlogger/lib/xlogger.js:169:9)
    at Request._callback (/usr/local/lib/node_modules/macaca-ios/node_modules/xctest-client/lib/proxy.js:58:18)
    at self.callback (/usr/local/lib/node_modules/macaca-ios/node_modules/xctest-client/node_modules/request/request.js:199:22)
    at emitOne (events.js:77:13)
    at Request.emit (events.js:169:7)
    at Request.onRequestError (/usr/local/lib/node_modules/macaca-ios/node_modules/xctest-client/node_modules/request/request.js:821:8)
    at emitOne (events.js:77:13)
    at ClientRequest.emit (events.js:169:7)
    at Socket.socketErrorListener (_http_client.js:269:9)
    at emitOne (events.js:77:13)
    at Socket.emit (events.js:169:7)
    at emitErrorNT (net.js:1269:8)
    at nextTickCallbackWith2Args (node.js:442:9)
    at process._tickCallback (node.js:356:17)