Support private repositories

[benmoss]

Putting this here just as a TODO resulting from #5

Private repos are not supported as of now.

I think it needs a little more work to fully support private repositories

Add a config preference in dotci configuration for enabling private repo setup.
Add deploy key to github repo when project is setup, and use that for git checkout.
Add configuration option to add deploy public key in dotci configuration.

[suryagaddipati]

DotCi-1.1.0 supports private repositories.
Installation instructions here.
https://github.com/groupon/DotCi/blob/master/docs/Installation.md#private-repository-configuration

[benmoss]

awesome!!