Remove #memcached_servers from endpoints.rb

Didn't like the fact `#memcached_servers` was inside endpoints.rb.
Also, didn't like db methods inside the default.rb, and how tests
were testing a default recipe, and a default library.  Felt this
should be cleaned up a bit into their own libraries.  This is prep
work to adding a method to return all rabbit servers for the HA
rabbit configuration.

Change-Id: I7d47f09547b04bc57b50a93e6d2f5f70539074c1