groupbytraceprocessor: TestPeriodicMetrics is unstable

[tigrannajaryan]

See https://app.circleci.com/pipelines/github/open-telemetry/opentelemetry-collector/3878/workflows/16e17361-807e-43fb-995a-3e5a517bdef2/jobs/42647

2020-10-08T22:10:41.128Z	DEBUG	groupbytraceprocessor/event.go:93	recording current state of the queue	{"num-events": 0}
--- FAIL: TestPeriodicMetrics (0.05s)
    event_test.go:411: 
        	Error Trace:	event_test.go:411
        	            				event_test.go:360
        	Error:      	Not equal: 
        	            	expected: int(1)
        	            	actual  : float64(2)
        	Test:       	TestPeriodicMetrics
    event_test.go:411: 
        	Error Trace:	event_test.go:411
        	            				event_test.go:366
        	Error:      	Not equal: 
        	            	expected: int(0)
        	            	actual  : float64(1)
        	Test:       	TestPeriodicMetrics

[tigrannajaryan]

@jpkrohling sorry, one more unstable, assigning to you.

[jpkrohling]

Windows again? Are the tests slower on Windows? I'll work on it, but it might be a good hint that perf tests on Windows might yield interesting results :-)

[tigrannajaryan]

Yes, Windows. Yes, possibly could be caused by a perf difference.

[jpkrohling]

@tigrannajaryan could you please move this to -contrib? I'm working on it right now.