config: import MuableMapping based on python version
config: import MuableMapping based on python version

MutableMapping has been moved from collections to collections.abc.

Signed-off-by: Rishabh Dave <d65d05ccb4d95d4cd49c1a041af3276370381a83@redhat.com>

ceph/teuthology,ceph/teuthology,ktdreyer/teuthology,ktdreyer/teuthology