crimson/osd: enable PGShardMapping access from all cores

crimson/osd: enable PGShardMapping access from all cores

Previously, all accesses (incuding loookups) had to occur on core 0.  Now that
we want to be able to dispatch from all cores, we need PGShardManager to be
accessible from all cores.  To that end, we now proxy updates to core 0, but maintain
local copies of the map so that cores can perform local lookups.

Signed-off-by: chunmei <chunmei.liu@intel.com>
(cherry picked from commit a3052969bfcfd9329b2baf7883765642d09ff038)