Make Dalli client server more flexible

Before it was only possible to use the host specified in bandit.yml (and
the port was ignored as well). Now, if the host isn't specified in the
config Dalli will properly fall back to using ENV["MEMCACHE_SERVERS"] or
127.0.0.1:11211.

See: https://github.com/mperham/dalli/blob/master/lib/dalli/client.rb#L29
Merge pull request #22 from swalkinshaw/dalli_server_improvements

Make Dalli::Client server more flexible