Fix 925-threadgroups when running on T.

Given we take metrics flags in priority from system properties, the flag
being passed through the 'run' script wasn't taking effect.

Make the test more robust by removing the metrics thread from the list
of threads we expect to see.

Test: 925-threadgroups
Change-Id: If15fe11a81af855c41a7c3c1bdb2f54edadc761c
3 files changed