Merge PR #21842 into master

* refs/pull/21842/head:
	MDSMonitor: clean up use of pending fsmap in uncommitted ops
	MDSMonitor: refactor last_beacons to use mono_clock
	mds: refactor MDSMap init
	mds: refactor FSMap init
	mds: refactor Filesystem init
	mds: move compat set methods to MDSMap

Reviewed-by: João Eduardo Luís <joao@suse.de>

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

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

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

diff --cc src/mon/FSCommands.cc
Simple merge

diff --cc src/mon/MDSMonitor.cc
Simple merge