generic/38[3-6]: require project quota to be enabled on SCRATCH_DEV

generic/38[3-6]: require project quota to be enabled on SCRATCH_DEV

generic/38[3-6] are made generic from xfs tests to test project
quota on other filesystems, e.g. ext4. But we should make sure
project quota is enabled in between of _scratch_enable_pquota and
_qmount. Otherwise mount will fail if there's no project quota
support on SCRATCH_DEV, e.g. ext2 and ext3.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>