MB-11367: Properly close all upr connections during shutdown

When we shutdown we need to close all streams before clearing out
all of the connections in the connection map.

Change-Id: I80679547c8ad9d278f5d6a3baac7668146dd012d
Reviewed-on: http://review.couchbase.org/38715
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>