mkfs: discard only after all validations

mkfs: discard only after all validations

Discard should happen only when everything has been validated, just
before we start writing to the device. If it happens earlier, it is
possible that mkfs will abort, but managed to already wipe data. This
patch moves the discard to the latest possible moment.

Signed-off-by: Jan Tulak <jtulak@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>