Merge PR #36448 into nautilus

* refs/pull/36448/head:
	mgr: Add python-enum34 dependency to package for older distributions
	mgr/volumes: Add documentation regarding --retain-snapshots option
	mgr/volumes: Avoid trashing retained subvolume on create errors
	mgr/volumes: Add subvolume v2 test cases
	mgr/volumes: Derive v2 from v1 to leverage common methods
	mgr/volumes: Introduce v2 subvolumes
	mgr/volumes: Use operation type during subvolume open

Reviewed-by: Venky Shankar <vshankar@redhat.com>
Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>