Merge PR #28082 into master

* refs/pull/28082/head:
	mgr / volumes: improve error handling
	py / cephfs: invoke base class Error::__init__() from OSError::__init__()
	mgr / volumes: carve out subvolume operations as a separate class
	mgr / volumes: introduce subvolume specification class
	mgr / volumes: carve of volume as a separate class