monc: backoff the timeout period when reconnecting

If the monitors are systematically slowing down, we don't want to spam
them with reconnect attempts every three seconds. Instead, every time
we issue a reconnect, multiply our timeout period by a configurable; when
we complete the connection, reduce that multipler by 50%. This should let
us respond to monitor load.
Of course, we don't want to do that for initial startup in the case of a
couple down monitors, so don't apply the backoff until we've successfully
connected to a monitor at least once.

Signed-off-by: Greg Farnum <greg@inktank.com>
OSD: disable the PGStatsAck timeout when we are reconnecting to a monitor

Previously, the timeout counter started as soon as we issued the reopen,
but if the reconnect process itself took a while, we might time out and
issue another reopen just as we get to the point where it's possible to
get work done. Since the mon client has its own reconnect timeouts (that is,
the OSD doesn't need to trigger those), we instead disable our timeouts
while the reconnect is happening, and then turn them back on again starting
from when we get the reconnect callback.

Signed-off-by: Greg Farnum <greg@inktank.com>