osd: change omap data encoding in object_copy_data_t

osd: change omap data encoding in object_copy_data_t

Pass the omap data in the struct as an opaque (encoded) bufferlist.  This
avoids a decode into an STL map, simplifying the crc calculation.  The
win isn't huge (yet) because we still turn it into a map to pass it down
to the ObjectStore method, but that too will change in time.

Signed-off-by: Sage Weil <sage@redhat.com>