Fix broken UprobeStatsTest

Make the test more reliable by killing the existing uprobestats
process if any is running and extending the timeout of waiting for the
output atom.

Test: atest android.cts.statsdatom.perf.UprobeStatsTest
Flag: TEST_ONLY
Bug: 378119072
Change-Id: I0157a32d863a769cf679f6cd1b5b0a8207e9550c