osdc/Objecter: ping osds for which we have pending commands

As with ops and linger_ops, this ensures we detect connection resets.

Signed-off-by: Sage Weil <sage@inktank.com>
osdc/Objecter: dump command ops

Dump command_ops along with everything else.

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