CM11 Themes: Fix how common resources are found

During the boot process, application info may not be fully
available and createPackageContext can throw a null pointer which
causes a theme's resource-cache to be cleared.  If this theme is
in /system/app or /system/priv-app the theme will still be installed
but applying it will result in styles not being applied.

Change-Id: I4094bdd923edc1d829024404a4ce1b72709bd4f1