More progress on triaging PackageManager callers.

Catch a bunch of simple cases where the PackageManager flags are
obvious.  Add the ability to use the MATCH_SYSTEM_ONLY flag on
PackageInfo and ApplicationInfo queries.

Re-examine recent tasks after a user is unlocked, since some of the
activities may now be available and runnable.

Bug: 26471205, 26253870
Change-Id: I989d9f8409070e5cae13202b47e2c7de85bf4a5b