Fix /data backup size if contains media subdirs

/data/*/media directories are mistakenly being excluded from the size
calculation. Change to absolute dir exclude so that only /data/media is
excluded.

Change-Id: I6e97604d44e6ea2bdf7dfd8c68a2f90ba6d44415
Merge "Fix /data backup size if contains media subdirs" into android-4.4