fix(registry): Use cache host and port from confd

The registry was crashing when trying to read cache
settings from unset environment variables.
confd is now also population those settings.

I also disabled the LRU cache as this requires a redis in LRU mode:
http://redis.io/topics/config
Merge pull request #728 from johanneswuerbach/fix-prod-registry

fix(registry): Use cache host and port from confd