btrfs: add optional parameter `ro' to btrfs_subvolume_snapshot

Parameter `ro' is for creating readonly btrfs snapshot.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Update gobject/Makefile.inc and POTFILES

Followup of commit 0b3c1762965f339915fd080884a61dbb36545204.
btrfs: add optional parameter `qgroupid' to btrfs_subvolume_snapshot

Parameter `qgroupid' is for adding the created snapshot to a qgroup.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
btrfs: add optional parameter `qgroupid' to btrfs_subvolume_create

Parameter `qgroupid' is for adding the created subvolume to a qgroup.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Update gobject/Makefile.inc and POTFILES

Followup of commit a120449c979993f4b5bd458ece00fadb339546d3.