tools: add ceph_monstore_tool with getosdmap

Signed-off-by: Samuel Just <sam.just@inktank.com>
PaxosService: use get and put for version_t

Otherwise, we just duplicate the logic for generating the version
key names.

Signed-off-by: Samuel Just <sam.just@inktank.com>
OSDMonitor: when adding bucket, delay response if pending map has name

Fixes: #4836
Signed-off-by: Samuel Just <sam.just@inktank.com>