mon mgr osd: Add dump_osd_times interface for python

mon mgr osd: Add dump_osd_times interface for python

The dump_osd_times interface is here for future use of a manager module.
The osd_stats and pg_dump python interfaces don't return network ping
information.

User facing ping time information is formatted 3 decimal places
Use dump_float() (low overhead) for network ping times
   used by python dump_osd_times and dump commands like
   "ceph --formet=json pg dump osds" which for now yields output like
   >>>> "1min": 0.61599999999999999,

Signed-off-by: David Zafman <dzafman@redhat.com>