mds: set l_mds_req on client request

This is one input for the load balancer.

Signed-off-by: Sage Weil <sage@redhat.com>
mds: rename a bunch of metrics

Also clean out a few that were unused and some dead code.

Signed-off-by: Sage Weil <sage@redhat.com>
mds/Server: rename perfcounters

Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2314 from ceph/wip-mds-pc

mds: clean up perfcounter names

Reviewed-by: John Spray <john.spray@redhat.com>