Unstable test: AsyncBarrierTests.StressMultipleGroups

From appveyor log:

[xUnit.net 00:00:12.1576651]     Microsoft.VisualStudio.Threading.Tests.AsyncBarrierTests.StressMultipleGroups(players: 2, groupSize: 1) [FAIL]
[xUnit.net 00:00:12.1588364]       System.TimeoutException : The operation has timed out.
[xUnit.net 00:00:12.1603051]       Stack Trace:
[xUnit.net 00:00:12.1662236]         C:\projects\vs-threading\src\Microsoft.VisualStudio.Threading\TplExtensions.cs(82,0): at Microsoft.VisualStudio.Threading.TplExtensions.<WithTimeout>d__5.MoveNext()
[xUnit.net 00:00:12.1663510]         --- End of stack trace from previous location where exception was thrown ---
[xUnit.net 00:00:12.1667640]            at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
[xUnit.net 00:00:12.1668505]            at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[xUnit.net 00:00:12.1669229]         C:\projects\vs-threading\src\Microsoft.VisualStudio.Threading.Tests\AsyncBarrierTests.cs(68,0): at Microsoft.VisualStudio.Threading.Tests.AsyncBarrierTests.<StressMultipleGroups>d__5.MoveNext()
[xUnit.net 00:00:12.1670373]         --- End of stack trace from previous location where exception was thrown ---
[xUnit.net 00:00:12.1671195]            at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
[xUnit.net 00:00:12.1671748]            at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[xUnit.net 00:00:12.1672228]         --- End of stack trace from previous location where exception was thrown ---
[xUnit.net 00:00:12.1672743]            at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
[xUnit.net 00:00:12.1673292]            at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[xUnit.net 00:00:12.1673762]         --- End of stack trace from previous location where exception was thrown ---
[xUnit.net 00:00:12.1674371]            at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
[xUnit.net 00:00:12.1674909]            at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
Failed   Microsoft.VisualStudio.Threading.Tests.AsyncBarrierTests.StressMultipleGroups(players: 2, groupSize: 1)
Error Message:
 System.TimeoutException : The operation has timed out.
Stack Trace:
   at Microsoft.VisualStudio.Threading.TplExtensions.<WithTimeout>d__5.MoveNext() in C:\projects\vs-threading\src\Microsoft.VisualStudio.Threading\TplExtensions.cs:line 82
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.VisualStudio.Threading.Tests.AsyncBarrierTests.<StressMultipleGroups>d__5.MoveNext() in C:\projects\vs-threading\src\Microsoft.VisualStudio.Threading.Tests\AsyncBarrierTests.cs:line 68
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)