New "frozen" state during app move/upgrade.

This replaces mOperationPending, which was in an odd place.  It adds
a new PackageSetting.frozen flag that is a last-ditch effort to
prevent ActivityManager from starting an app while it's being moved
or upgraded.

Also provides clearer guarding around all upgrades by freezing,
killing, upgrading, then unfreezing.

Bug: 20275579
Change-Id: I28bb0359a6f4e05080fb336b18dd2a249509d989