kinesis.ShardReadersPoolTest.shouldInterruptKinesisReadingAndStopShortly is flaky

This appears to be unavoidable due to the construction of the test - the amount of realtime that the thread waits is asserted to be less than one second, but as the class doesn't consume a Ticker (or related way to track elapsed time), we have no way of deterministically controlling that value within the test.

Example failure: https://builds.apache.org/job/beam_PreCommit_Java_GradleBuild/1738/testReport/junit/org.apache.beam.sdk.io.kinesis/ShardReadersPoolTest/shouldInterruptKinesisReadingAndStopShortly/

java.lang.AssertionError: Expecting: <4169L> to be less than: <1000L> at org.apache.beam.sdk.io.kinesis.ShardReadersPoolTest.shouldInterruptKinesisReadingAndStopShortly(ShardReadersPoolTest.java:159) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 

The test could also do with a more precise error message (it looks like too many elements were received based on the error message, rather than the actual "took too long" failure.