pm: Fix lock insanity with ActivityManager

 * It's possible that ActivityManager may be trying to stop a package
   while the PackageManager is trying to perform a scan during
   an upgrade. When AM tries to perform the stop, it will attempt
   to look up the package user, which will try to take the PM lock.
   This is fine, but while we're holding the lock in PM during
   the package upgrade we're attempting to call back into AM to
   get the current theme, which tries to take the AM lock. This
   results in the entire system locking up until watchdog kills
   off system server.
 * Instead of looking up the current theme while holding the lock
   in PM, look it up before locking the whole place down.

Change-Id: If322a7f214218740d73043ff65860ccadd92f01d