Add a unit test for ChangeReporter.

Separate the decision on whether to log to two separate ones - logcat
and statsLog to allow separate policies.
Also add startLogAll and endLogAll in preparation for an adb command
that will enable/disable logging to logcat every time.

Test: atest ChangeReporterTest
Bug: 138374585
Bug: 140910281

Change-Id: Ie49368b838a19845f51a2670035f611d3e4b9a1b