mon: dump MonitorDBStore transactions to file

Signed-off-by: Samuel Just <sam.just@inktank.com>
ceph-monstore-tool: add MonitorDBStore trace dumper

Signed-off-by: Samuel Just <sam.just@inktank.com>
ceph-monstore-tool: added replay
mon: set MonitorDBStore options on open

So both ctors set the options.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #265 from ceph/wip-mon-trace