Make thread leak error message more readable

This change only outputs thread count differences instead of
listing all threads. Additionally, it ignores threads with 1
count, which effectively filter out threads created
by the test runner or other system components, such as
hwuiTask*, queued-work-looper, SurfaceSyncGroupTimer,
RenderThread, and Time-limited test.

Sample Output:
[1122/3060] android.net.connectivity.com.android.server.CSLocalAgentCreationTests#ThreadLeakMonitor: FAILED (1ms)

STACKTRACE:
java.lang.IllegalStateException: Unexpected thread changes: removed=[] added=[] updated=[TestAlarmManager=25,CSTestHandler=25]

Test: atest ConnectivityCoverageTests
      (with shouldThreadLeakFailTest set to true)
Bug: 310581973
Bug: 307693729
Change-Id: I085799ebbd69c29f833335684de208105302e012