pybind/mgr/rbd_support: delay creation of progress event

pybind/mgr/rbd_support: delay creation of progress event

Create the progress module event upon receipt of the first
progress callback from the librbd API. This will help to ensure
that all prereqs have been validated for retryable errors like
scheduling an image to be removed while it still has attached
cloned children.

Fixes: https://tracker.ceph.com/issues/48296
Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit c0069b00e4748974d4bf5cfa1bdab68d6f043abb)

Conflicts:
        src/pybind/mgr/rbd_support/task.py
- file does not exist in nautilus: applied the changes manually