Allow to skip occasionally hanging test from environment
Allow to skip occasionally hanging test from environment

The MB19748TestDeleteWhileConnShipLogAndFullWriteBuffer test frequently
(almost always!) hangs on my system. It would be simpler to just skip
this test conditionally from the environment, so as to allow `make
test`, `ctest`, and so on to function normally.

Change-Id: I331fdc6d5a10b378b0956d8499865081a7f8ca49
Reviewed-on: http://review.couchbase.org/72205
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,couchbase/memcached,daverigby/memcached,daverigby/memcached,daverigby/memcached,couchbase/memcached,daverigby/kv_engine,daverigby/memcached,couchbase/memcached,daverigby/kv_engine,daverigby/kv_engine,couchbase/memcached