msgr: add get_loopback_connection() method

Return the Connection* for ourselves, so we can queue messages for
ourselves.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: requeue osdmaps on heartbeat connections for cluster connection

If we receive an OSDMap on the cluster connection, requeue it for the
cluster messenger, and process it there where we normally do.  This avoids
any concerns about locking and ordering rules.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: pass new maps to dead osds via existing Connection

Previously we were sending these maps to dead osds via their old addrs
using a new outgoing connection and setting the flags so that the msgr
would clean up.  That mechanism is possibly buggy and fragile, and we can
avoid it entirely if we just reuse the existing heartbeat Connection.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: share incoming maps via Connection*, not addrs

Kill a set of parallel methods that are using the old addr/inst-based
msgr APIs, and instead use Connection handles.  This is much safer and gets
us closer to killing the old msgr API.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: kill unused addr-based send_map()

Not used, old API, bad.

Signed-off-by: Sage Weil <sage@inktank.com>
osd/PG: include map epoch in query results

Currently you can only infer it from the info.history.* fields.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge branch 'wip-osd-msgr'

Reviewed-by: Samuel Just <sam.just@inktank.com>