Keystore2: Wait for statsd to be available before calling statsd_write()

This is to avoid errors being printed at keystore2 startup due to
statsd not being available.
(refer b/185844285#comment13 for other options for avoiding this)

Also, removed watch dog watch point in async_task since waiting for
boot completion takes a lot of time, triggering watch dog.

Also changed register_pull_metrics_callbacks to use
wait_for_boot_completed and be called in async_task.

Bug: 188441750
Test: statsd Test Drive script for all three types of atoms.
keystore2 startup logs.
Merged-In: I41b48526aad9702dd29f93d139e5f2afba89be3a

Change-Id: I41b48526aad9702dd29f93d139e5f2afba89be3a
3 files changed