Simplify ssh key usage with whilp/ssh-agent and yaml syntax

[rosskevin]

See http://stackoverflow.com/questions/32897709/ssh-agent-forwarding-inside-docker-compose-container/32911979#32911979

Similar to gems, this uses a long running volume. Perhaps we can inject an interpolated single ssh-agent container into the yaml for use, with a single command, then clean it up afterwards?

[rosskevin]

Do something similar to #20

# Make the host user's id_rsa key available to the web container e.g. for cloning from github
ssh-agent:
  containers:
    - web
  keys:
    - id_rsa

Should generate a seed default config of

compose:
  web:
    environment:
      # make ssh keys available via ssh forwarding (see volume entry)
      - SSH_AUTH_SOCK=/root/.ssh/socket

    volumes_from:
      # Use configured whilp/ssh-agent long running container for keys
      - ssh-agent

It will also create the container and populate it with keys, prior to up. I think we need to use a project_name based name for the ssh container though, and clean it up, unless we want our keys in a volume sticking around...

[rosskevin]

Unknown hosts are still a problem (anything from bitbucket or github). Both of these fail with "Host key verification failed"

ssh -o 'StrictHostKeyChecking no' -T git@github.com
ssh -o 'StrictHostKeyChecking no' -T git@bitbucket.org

But these succeed

ssh -o 'StrictHostKeyChecking no' -T git@github.com
ssh -o 'StrictHostKeyChecking no' -T git@bitbucket.org

Need to figure out a way to either share ssh/config with an exclusion or known_hosts.

[rosskevin]

As of daea2fc, this issue is solved, requires merging (or local building) of whilp/ssh-agent#3

[rosskevin]

Fixed in 0.7.1