Merge pull request #2043 from guangyy/wip-pg-splitting

Support 'expected_num_objects' parameter when creating pool for pg folder splitting

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

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

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

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