shared/032: handle mkfs.* in either /sbin or /usr/sbin

shared/032: handle mkfs.* in either /sbin or /usr/sbin

mkfs executables may live in either /sbin or /usr/sbin, and
the current regexp in this test only catches the former,
and so the test won't run properly with the latter.

Fix this by filtering out whatever was found as
${MKFS_PROG}, rather than a hard-coded /sbin/mkfs path.

Because the list was generated by using a wildcard
with ${MKFS_PROG}.* this will always be the correct filter.

Reported-by: Boaz Harrosh <boaz@plexistor.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>