librbd: validate data pool for self-managed snapshot support

librbd: validate data pool for self-managed snapshot support

Fixes: https://tracker.ceph.com/issues/24675
Signed-off-by: Mykola Golub <mgolub@suse.com>
(cherry picked from commit 08ea7d62ba6eedf614d72ff9d33f2e6a1c0b81fe)

Conflicts:
	src/librbd/image/CreateRequest.cc
	src/librbd/image/CreateRequest.h
- luminous uses m_ioctx where master has m_io_ctx
- luminous IoCtx does not have get_namespace/set_namespace
- in luminuos CreateRequest state machine is a little different than in
the master (see the diagram in CreateRequest.h). In luminous the next
state after VALIDATE_DATA_POOL is CREATE_ID_OBJECT, so call
create_id_object() instead of add_image_to_directory().