sensu-go: Custom / extended attributes not working with agent yaml config

Expected Behavior

Should be able to pass extended attributes using either command line, or json/yml file.

Current Behavior

Custom attributes are not passed

Steps to Reproduce (for bugs)

Tried to set the attributes in several ways (according to the doc) : Dummy client agent.yml :

---
##
# agent configuration
##
id: "test.machine"
#organization: "default"
#environment: "default"
subscriptions:
backend-url:
  - "ws://myserver:8081"

testattr1: "test"

extended_attributes:
  testattr2: "test123"

##
# authentication configuration
##
user: "agent"
password: "superpassword"

##
# other
##
cache-dir: "~/sensu/cache"

Running it with command : sensu-agent start -c agent.yml --custom-attributes "testattr3: test"

sensuctl entity info test.machine --format json output :

{
  "class": "agent",
  "deregister": false,
  "deregistration": {},
  "environment": "default",
  "id": "test.machine",
  "keepalive_timeout": 120,
  "last_seen": 1535095375,
  "organization": "default",
  "redact": [
    "password",
    "passwd",
    "pass",
    "api_key",
    "api_token",
    "access_key",
    "secret_key",
    "private_key",
    "secret"
  ],
  "subscriptions": [
    "entity:test.machine"
  ],
  "system": {
    "hostname": "pc1-ps002",
    "os": "linux",
    "platform": "ubuntu",
    "platform_family": "debian",
    "platform_version": "18.04",
    "network": {
      "interfaces": [
        {
          "name": "lo",
          "addresses": [
            "127.0.0.1/8",
            "::1/128"
          ]
        },
        {
          "name": "enp0s31f6",
          "mac": "30:9c:23:70:5d:a3",
          "addresses": [
            "10.252.36.30/22",
            "fe80::d8f3:ac37:47a2:74e7/64"
          ]
        },
        {
          "name": "anbox0",
          "mac": "ea:8c:b9:08:39:e3",
          "addresses": [
            "192.168.250.1/24",
            "fe80::e88c:b9ff:fe08:39e3/64"
          ]
        },
        {
          "name": "docker0",
          "mac": "02:42:0b:58:21:3a",
          "addresses": [
            "172.17.0.1/16",
            "fe80::42:bff:fe58:213a/64"
          ]
        },
        {
          "name": "br-e907becf2e0f",
          "mac": "02:42:ed:71:56:69",
          "addresses": [
            "172.19.0.1/16",
            "fe80::42:edff:fe71:5669/64"
          ]
        },
        {
          "name": "br-fd51f7f7a5da",
          "mac": "02:42:09:62:10:b9",
          "addresses": [
            "172.18.0.1/16"
          ]
        },
        {
          "name": "vethd2d58e2",
          "mac": "7a:39:c9:c0:d4:c1",
          "addresses": [
            "fe80::7839:c9ff:fec0:d4c1/64"
          ]
        }
      ]
    },
    "arch": "amd64"
  },
  "user": "agent"
}

As you can see, none of the testattr are displayed here.

Context

Unable to use custom attributes as tokens

Your Environment

sensu-agent : sensu-agent version 2.0.0-beta.4-4#a05ad41, build a05ad411199077286f49c06629eed4823331176c, built 2018-08-16T21:25:14+0000 Running on Ubuntu 18.04

sensu-backend : sensu-backend version 2.0.0-beta.4-4#a05ad41, build a05ad411199077286f49c06629eed4823331176c, built 2018-08-16T21:23:57+0000 Running on Centos 7.5