Improve CounterTrack perf test

This patch makes the following changes:

1. Add **average time** to *all* perf test outputs.
2. **Reduce noise & time** by using *counter_tracks.html* instead of *android_systrace.html* in the <tt>CounterTrack</tt> perf test.
3. **Restart scaling** for every iteration in the <tt>CounterTrack</tt> perf test.
4. **Select** half of all counter **samples** in the <tt>CounterTrack</tt> perf test.