CBQE-0: stop load thread if enospc is reached

Change-Id: Ifc1f19d46d95d3b76918052c9247366e7928a94c
Reviewed-on: http://review.couchbase.org/26408
Reviewed-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>
Tested-by: buildbot <build@couchbase.com>