Sanity-check paths of files to be restored

The duplicated implementations are an artifact of an ongoing
refactor of the full-data restore code.  The adb-specific path
will be switched to use the FullRestoreEngine [as has already
been done for the 'adb backup' path using the parallel full
backup engine], at which point the extra implementation here
will be removed, but for now we need to make sure that all
bases are covered.

Bug 16298491

Change-Id: I9cdb8a1c537939a620208df3cf0e921061b981ad