toolbox: Add levelFromUid categorization support to restorecon

This is necessary for the app data relabeling on migrated devices
to include the proper app context. Freshly installed apps get this
done automagically, as do newly created files.

Change-Id: If7421dac01c6ae8bd78e66f71e69298ed850a7ab
fs_mgr: Drop the context mount option from non-selinux builds

This will require that transitioning devices have context as the
last mount option, since everything after it will be ignored

Change-Id: Ic5cc7f5632cc3d62459dfaaf7719d662737e1641