client: track osd epoch barrier

Signed-off-by: John Spray <john.spray@redhat.com>
mds: implement osd epoch barrier on caps

Signed-off-by: John Spray <john.spray@redhat.com>
mds: add 'osdmap barrier' admin command

This is for use with client eviction.

Signed-off-by: John Spray <john.spray@redhat.com>
osdc: continuously subscribe to osd map on pause

We were doing this on FULL, should also have done it
on PAUSERD and PAUSEWR, to avoid paused requests
staying that way forever.

Signed-off-by: John Spray <john.spray@redhat.com>
client: add 'status' asok

Useful in test/debug for querying OSD epoch
and OSD barrier epoch.

Signed-off-by: John Spray <john.spray@redhat.com>
osdc/Objecter: add have_map method

This is for places we're going to call wait_for_map, so
that we can easily check if we will *probably* get
a true from wait_for_map, and thereby avoid
allocating Contexts we won't need.

Signed-off-by: John Spray <john.spray@redhat.com>
wip include epoch in reconnect