Fix new ASAN issues highlighted by C++14 upgrade

As part of upgrading to the C++14 standard, there have been multiple new ASAN issues identified which should be addressed and fixed.

Couple of example jobs:

http://cv.jenkins.couchbase.com/job/kv_engine-addresssanitizer-master/1475/consoleFull#1392194346b106e815-6d27-4a01-8b14-4b94513c99be

http://cv.jenkins.couchbase.com/job/kv_engine-addresssanitizer-master/1471/consoleFull#1392194346b106e815-6d27-4a01-8b14-4b94513c99be