Rake tasks that operate with a remote stack's ENV (via ow:config:from_env) should also be able to connect to the memcached server, if available.

This copies the first available online memcached instance's private IP
into the MEMCACHE_SERVERS environment variable, which is where the
Dalli client looks for it, by default. In case the calling code can't
access the private IP, the public host is copied into
MEMCACHE_SERVERS_PUBLIC.