ovsdb: Log when remote connections are deconfigured.

ovsdb: Log when remote connections are deconfigured.

Recently I helped debug a scenario where ovsdb-server connected to a remote
manager, then ovs-vsctl deleted the remote manager and soon after re-added
it.  The log was difficult to interpret because it showed two successful
connection attempts to the same remote without showing a reason why the
connection was dropped in the first place.  Adding this log message would
make it clear that the configuration changed to remove that remote
connection in the meantime.