DiskStats Westworld Migration

Migrates the existing information collected by diskstats to westworld.
Creates 4 pulled atoms, 2 of which read from a cached file produced by
DiskStatsLoggingService. Most of the logic is taken from
DiskStatsService.java.

Test: Manually verified information is the same as dumpsys. Will look
into cts as well.

Change-Id: I9818ac787de46514bc09ab3887cbfaec6cff273c