E2e test for count metric anomaly on config update

Mocks out IPendingIntentRef to properly e2e test alerts firing and
informing the subscriptions. (The previous tests only asserted that the
alert was in refractory period). Test preserving an alert preserves
history and refractory period, that building a new alert on an existing
metric works, and that removing/replacing alerts works.

Test: atest statsd_test
Bug: 174976680
Change-Id: I06f3b08068159d6ca123468578be167e29fefc1a
7 files changed