Fix Statsd rejecting configs

Statsd is rejecting configs for two reasons as a result of the new
puller API:

1. It expected all of the required pullers to be in the puller map when
the config was sent. This is no longer required to be true since the map
is updated as pullers are registered. Most significantly, no pullers
will be present on boot when we parse the config.

2. In metrics_manager_util, we would create a StatsPullerManager on the
local stack and check that for the puller existing, rather than the sp<>
that was passed in. Since we changed the big puller map to be non-static
in ag/10174227, checking the map from the local pullerManager is
guaranteed to fail, since none of the pullers are added to that puller
manager.

This Cl fixes both issues.

Bug: 148405638
Test: added the config used in b/148405638. Made sure it was valid when
pushed on boot, and at some point after boot after the pullers
registered.

Change-Id: If083bda03b5db2822347d518bba23573b573bf89