Adding a BACKEND_ADDITIONS environment variable

This is up for discussion, I'm not thrilled with this way of accomplishing this and want to see what, if any, are your plans to support non-linked containers. Currently, it doesn't help me a ton to load balance between two running containers on the same physical host. I could set up ambassador containers, but I'm nto sure I see the point when we can just use SSL to encrypt connections to the backend and then they can be anywhere. 

This patch allows for a simple BACKEND_ADDITIONS environment variable to be passed into the container at runtime and should not be mutually exclusive to linked containers. 

For example I run: 

docker run -d -p 0.0.0.0:1234:443 -e BACKEND_ADDITIONS="$(cat /home/core/stresler/env_files/backend_additions.txt)" -e SSL_CERT="$(cat /home/core/stresler/env_files/testtest.pem)" -e PORT=443 eae4e9667f53 

where backend_additions.txt contains: 

server portal_1 12.34.56.789:443 check ssl verify none

and the container can now load balance, with SSL, to any available server. 

I'm guessing that this won't work with the tutum service detection as-is, though. I imagine on the backend you're using something like etcd to store the current members of a tutum load balanced pool. 

What are your thoughts on this?