MediaScanner: Ignore dirs with .noscanandnomtp

Completely ignore directories with .noscanandnomtp files
in them. Placing a .nomedia file will still scan a
directory but exclude it from the media database. This
is so the file may still be presented for MTP purposes.

Placing .noscanandnomtp completely prevents the scan,
which saves considerable processing power and battery
life on systems with numerous media files, but prevents
them from being seen over MTP.

Change-Id: Ibff2a9f2525255a2ac34132eeee36734962fbdd7