Use Event in streaming test

Based on comments in Ia153e2d436855dcce256d5fc91d0fd4c47116042 we
add some synchronization around the streaming thread used in the
TestStreaming.test_streaming unit test.

Also fix a style nit.

Change-Id: I673611c01862137f5169f768a30f1b3a60bfbd7d
1 file changed