MB-9922: crash vbucket xmem replicator on xdcr certificate update

I.e. so that we're never replicating in plain when ssl is needed.

Change-Id: Id41c5fa10739b1e6af9f54103c04914cce29bcbf
Reviewed-on: http://review.couchbase.org/32498
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>