generic: use _qmount_option and _qmount

generic: use _qmount_option and _qmount

This commit touches generic tests call `_scratch_mount -o usrquota`
then chmod 777, quotacheck and quotaon. They can be simpilfied
to _qmount_option and _qmount. _qmount already calls quotacheck,
quota and chmod ugo+rwx. The conversions can save a few lines.

Signed-off-by: Su Yue <glass.su@suse.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>