Intermittent DCP testsuite failure

The DCP tests are now intermittently failing at a reasonably high frequency:

http://factory.couchbase.com/view/build/view/commit_validation/view/ep-engine/job/ep-engine-gerrit-master-multi/2169/label_exp=sherlocker-ubuntu12.04/console
http://factory.couchbase.com/view/build/view/commit_validation/view/ep-engine/job/ep-engine-gerrit-master-multi/2167/label_exp=sherlocker-ubuntu12.04/console
http://factory.couchbase.com/view/build/view/commit_validation/view/ep-engine/job/ep-engine-gerrit-master-multi/2162/label_exp=sherlocker-ubuntu12.04/console
http://factory.couchbase.com/job/ep-engine-threadsanitizer-master/1387/testReport/junit/(root)/projectroot/ep_engine_full_eviction_dcp/

This appears to occur more often now that the DCP tests are in their own testsuite and when running tests in parallel.

Example (Although the exact error tends to vary):

1

00:44:40.397 /home/couchbase/jenkins/workspace/ep-engine-gerrit-master-multi/label_exp/sherlocker-ubuntu12.04/ep-engine/tests/ep_testsuite_dcp.cc:1511 Test failed: `Unexpected DCP operation: ' (false)