MB-12238: set timeout of 10 minutes on xmem requests

As another measure against possible issues when NAT between DCs
forgets about our connections. With this patch, if this happens, xdcr
will still get stuck, but it won't last too long due to timeout. When
timeout hits, affected xdcr replicators will crash and be restarted
have a decent chance of working.

Change-Id: I30e07c1ab8e73a79d5aa0502c3e39e2bb59c7ce0
Reviewed-on: http://review.couchbase.org/41588
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>