Merge pull request #5931 from ceph/wip-cxx11concurrency

librados: move to c++11 concurrency types

Reviewed-by: Matt Benjamin <mbenjami@redhat.com>
Reviewed-by: Casey Bodley <cbodley@redhat.com>

diff --cc src/CMakeLists.txt
Simple merge

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

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

diff --cc src/test/CMakeLists.txt
Simple merge