Improve behavior of bg check.

There is a new APP_START_MODE_DELAYED_RIGID which means that
things discovering something is not allowed to start should
report a clear error back to the caller.  This is how apps
that opt in to bg check should behave, and will now
be used if the app op mode is set to ERRORED.

This (for now?) removes the code that allows services to
be started if the request is coming from a foreground process.
That behavior isn't in the current bg check spec, and
probably not what we want as the standard platform model (since
it makes knowing when a service can start even harder to
determine).  It was originally done for the experimental
bg check work in N to see how much we could avoid
breaking existing apps, so not relevant when apps need to
explicitly opt in.

Also report temporary whitelist changes to activity manager for
it to lift background restrictions temporarily for apps.  Being
on the whitelist is now part of UidRecord, preventing a uid from
going idle.

Test: Initial CTS test added.

Change-Id: I36fd906fa69de8b7ff360605ae17c088f182e172