Log keystore key creation events using statsd.

This is the first CL on migrating keystore logging to use statsd.
This migrates the logging for key creation events
	(generation/import).
A work-around is implemented to handle repeated fields via bitmaps
	because statsd does not support repeated fields as of now.

Test: Adding tests for logging is yet to be decided.
Bug: 157664923
Change-Id: I76900eb2abec627afb80573cda25340186e9f244

Change-Id: Id23724cfbd21dca8ef5fd77e5712c0bc2e727f4b
8 files changed