Merge pull request #1139 from ceph/wip-agent

osd: basic cache tier agent

Reviewed-by: Samuel Just <sam.just@inktank.com>

diff --cc src/mon/MonCommands.h
Simple merge

diff --cc src/osd/OSD.cc
Simple merge

diff --cc src/osd/OSD.h
Simple merge

diff --cc src/osd/ReplicatedPG.cc
Simple merge