ceph_test_librbd: support value-parameterized tests for different format

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
ceph_test_librbd: add RBD_FEATURE_IMAGEINDEX feature tests

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
ImageIndex: Let load snapshot image index when changing snap

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
rbd: Add single-client support for rbd

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
fsx: support singleclient flag

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>
ImageIndex: fix when clone image's order is different from parent

Signed-off-by: Haomai Wang <haomaiwang@gmail.com>