MB-12644:bp: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.

Orig-Reviewed-on: http://review.couchbase.org/41588

Conflicts:
	src/pooled_memcached_client.erl
	src/xdc_vbucket_rep_xmem.erl

Change-Id: I3c8a96d71bcb983be5e804c3e6e8eaaf7be4e7b4
Reviewed-on: http://review.couchbase.org/43231
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>