Fix race condition in tests #502

Job	Run time
build-demos (BenchmarkIPhone)	1s
build-demos (BenchmarkMac)	1s
build-demos (CLI)	1s
build-demos (CaptureASL)	1s
build-demos (ContextFilter)	1s
build-demos (CoreDataLogger)	1s
build-demos (CustomFormatters)	1s
build-demos (CustomLogLevels)	1s
build-demos (DispatchQueueLogger)	1s
build-demos (FineGrainedLogging)	1s
build-demos (GlobalLogLevel)	1s
build-demos (LogFileCompressor)	1s
build-demos (NonArcTest)	1s
build-demos (OverflowTestMac)	1s
build-demos (PerUserLogLevels)	1s
build-demos (RegisteredLoggingTest (Desktop))	1s
build-demos (RegisteredLoggingTest (Mobile))	1s
build-demos (RollingTestMac)	1s
build-demos (SQLiteLogger)	1s
build-demos (TestXcodeColors (Desktop))	1s
build-demos (TextXcodeColors (Mobile))	1s
build-demos (UniversalApp)	1s
build-demos (WebServerIPhone)	1s
	23s

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