MB-19260: Make cookie atomic to serialize set/get in ConnHandler

MB-19260: Make cookie atomic to serialize set/get in ConnHandler

WARNING: ThreadSanitizer: data race (pid=20056)

  Write of size 8 at 0x7d600000f038 by main thread (mutexes: write M1412):
    #0 ConnHandler::setCookie(void const*) /home/abhinav/couchbase/ep-engine/src/tapconnection.h:344 (ep.so+0x000000042367)
    #1 EventuallyPersistentEngine::createTapQueue(void const*, std::string&, unsigned int, void const*, unsigned long) /home/abhinav/couchbase/ep-engine/src/ep_engine.cc:2655 (ep.so+0x0000000b86da)
    #2 EvpGetTapIterator(engine_interface*, void const*, void const*, unsigned long, unsigned int, void const*, unsigned long) /home/abhinav/couchbase/ep-engine/src/ep_engine.cc:1462 (ep.so+0x0000000b46a3)
    #3 mock_get_tap_iterator(engine_interface*, void const*, void const*, unsigned long, unsigned int, void const*, unsigned long) /home/abhinav/couchbase/memcached/programs/engine_testapp/engine_testapp.cc:467 (engine_testapp+0x0000000bae3e)
    #4 test_tap_ack_stream(engine_interface*, engine_interface_v1*) /home/abhinav/couchbase/ep-engine/tests/ep_testsuite.cc:7341 (ep_testsuite.so+0x000000050416)
    #5 execute_test(test, char const*, char const*) /home/abhinav/couchbase/memcached/programs/engine_testapp/engine_testapp.cc:1090 (engine_testapp+0x0000000b946c)
    #6 __libc_start_main /build/buildd/eglibc-2.19/csu/libc-start.c:287 (libc.so.6+0x000000021ec4)

  Previous read of size 8 at 0x7d600000f038 by thread T9 (mutexes: write M1411):
    #0 ConnHandler::getCookie() const /home/abhinav/couchbase/ep-engine/src/tapconnection.h:340 (ep.so+0x00000004067c)
    #1 bool TapConnMap::performOp<Item*>(std::string const&, TapOperation<Item*>&, Item*) /home/abhinav/couchbase/ep-engine/src/connmap.h:389 (ep.so+0x00000001fa08)
    #2 ItemResidentCallback::callback(CacheLookup&) /home/abhinav/couchbase/ep-engine/src/backfill.cc:63 (ep.so+0x00000001d9ca)
    #3 CouchKVStore::recordDbDump(_db*, _docinfo*, void*) /home/abhinav/couchbase/ep-engine/src/couch-kvstore/couch-kvstore.cc:1654 (ep.so+0x000000180ca0)
    #4 recordDbDumpC(_db*, _docinfo*, void*) /home/abhinav/couchbase/ep-engine/src/couch-kvstore/couch-kvstore.cc:66 (ep.so+0x00000017fe95)
    #5 lookup_callback(couchfile_lookup_request*, _sized_buf const*, _sized_buf const*) /home/abhinav/couchbase/couchstore/src/couch_db.cc:767 (libcouchstore.so+0x00000000d7e5)
    #6 btree_lookup_inner(couchfile_lookup_request*, unsigned long, int, int) /home/abhinav/couchbase/couchstore/src/btree_read.cc:99 (libcouchstore.so+0x00000000b5a2)
    #7 btree_lookup /home/abhinav/couchbase/couchstore/src/btree_read.cc:131 (libcouchstore.so+0x00000000affc)
    #8 couchstore_changes_since /home/abhinav/couchbase/couchstore/src/couch_db.cc:812 (libcouchstore.so+0x00000000d5f1)
    #9 CouchKVStore::scan(ScanContext*) /home/abhinav/couchbase/ep-engine/src/couch-kvstore/couch-kvstore.cc:1264 (ep.so+0x00000017f94e)
    #10 BackfillDiskLoad::run() /home/abhinav/couchbase/ep-engine/src/backfill.cc:131 (ep.so+0x00000001e449)
    #11 ExecutorThread::run() /home/abhinav/couchbase/ep-engine/src/executorthread.cc:112 (ep.so+0x0000000f8956)
    #12 launch_executor_thread(void*) /home/abhinav/couchbase/ep-engine/src/executorthread.cc:33 (ep.so+0x0000000f84f5)
    #13 platform_thread_wrap /home/abhinav/couchbase/platform/src/cb_pthreads.c:23 (libplatform.so.0.1.0+0x000000003d31)

Change-Id: I8a668f17013c95abc9786d853ed2c6462cae5320
Reviewed-on: http://review.couchbase.org/62978
Well-Formed: buildbot <build@couchbase.com>
Reviewed-by: Will Gardner <will.gardner@couchbase.com>
Tested-by: buildbot <build@couchbase.com>