VID-516 Add logging and reduce cache ttl

Add logging wherever we set fileExists to false to try to trap the condition where the file does actually exist, but memcache has fileExists === false set.

Also reduce the ttl for the cache in the case where fileExists is false so that this problem will be reduced while this problem is investigated.
VID-516 Remove the quick fix.  Want to see the problem occuring while the logging is in place
VID-516 A little more debugging
Merge pull request #1053 from Wikia/VID-516-CachedAbsence

Vid 516 cached absence