upr client: handle gen_tcp send and recv errors

Change-Id: Ie97d2d1815e911424e6c1984f0fc26c59fd7ea53
Reviewed-on: http://review.couchbase.org/34153
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>