Merge PR #24797 into master

* refs/pull/24797/head:
	mds: handle state change race

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

diff --cc src/mds/Locker.cc
Simple merge

diff --cc src/mds/MDCache.cc
Simple merge

diff --cc src/mds/MDSRank.cc
Simple merge

diff --cc src/mds/MDSRank.h
Simple merge