misc: use libmagic when libblkid can't identify something

If we're using check_plausibility() to try to identify something that
obviously isn't an ext* filesystem and libblkid doesn't know what it
is, try libmagic instead.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
13 files changed