Add the abilty to provide a config file for the proxy command.
docopt not honoring default value.
Be able to turn off strict host checking.
Remove continuous-integration.yml which no longer exists.
Be able to place a read-only ssh credential for the jenkins instance.

Also add two more useful plugins.
Update the ruby role for issues found while testing jenkins role.

In certain states, ruby is installed but the env is not setup so it is importart
to always run the environment update task and the rehash task.

The rbenv install task prompts if the version of ruby is already installed. This
freezes the build so skip it if the version directory already exists.
Correct NAT Backup Image type.
Merge pull request #227 from edx/feanil/provision-vpc

Feanil/provision vpc