runtime: [HttpListener] Hang of System.Net.HttpListener.Tests in CI

https://ci.dot.net/job/dotnet_corefx/job/master/job/ubuntu14.04_debug_prtest/8257/consoleFull#130661499679494335-f7bd-47d0-8771-8661e00c2db2

22:05:43   Finished running tests. End time=05:05:43. Return value was 0
23:44:38 
Build timed out (after 120 minutes). Marking the build as aborted.
23:44:38 
Build was aborted
23:44:38 [xUnit] [INFO] - Starting to record.
23:44:38 [xUnit] [INFO] - Processing xUnit.Net-v2 (default)
23:44:38 
MSBUILD : error MSB4166: Child node "2" exited prematurely. Shutting down. Diagnostic information may be found in files in the temporary files directory named MSBuild_*.failure.txt.
23:44:38 [xUnit] [INFO] - [xUnit.Net-v2 (default)] - 155 test report file(s) were found with the pattern 'bin/**/testResults.xml' relative to '/mnt/j/workspace/dotnet_corefx/master/ubuntu14.04_debug_prtest' for the testing framework 'xUnit.Net-v2 (default)'.
23:44:38 /mnt/j/workspace/dotnet_corefx/master/ubuntu14.04_debug_prtest/Tools/tests.targets(345,5): warning MSB5021: "sh" and its child processes are being terminated in order to cancel the build. [/mnt/j/workspace/dotnet_corefx/master/ubuntu14.04_debug_prtest/src/System.Net.HttpListener/tests/System.Net.HttpListener.Tests.csproj]
23:44:39 Command execution failed with exit code 143.

Not actionable based on this information, but starting an issue.