Fix ConnectivityServiceTest testRequestBenchmark

This patch fixes flakyness of testRequestBenchmark by adjusting time
limit for callback registration from 100ms to 180ms, and time limits for
onAvailable and onLost triggers from 30ms to 40ms.

With these timeouts the test succeeds 100% over 5000 iterations.

When using 150ms for registration timeout, running the test 5000 times
fails 2 times.

When using 30ms for onLost timeout, running the test 5000 times fails
1 times.

In addition, this patch also cleans testRequestBenchmark and uses the
more stable SystemClock.elapsedRealtime() for duration measurements.

Test: $ runtest frameworks-net
Bug: 32561414
Change-Id: I7601b2f1f11f83914f885a74c8a376173eed186b