Fallback to NATs if staging over http isn't there

[fraenkel]

Thanks for contributing to the cloud_controller_ng. To speed up the process of reviewing your pull request please provide us with:

• A short explanation of the proposed change:
  When staging over http isn't supported on the DEA, fallback to NATs
• An explanation of the use cases your change solves
  Rolling upgrade when CC supports staging and the DEAs don't yet.
• I have viewed signed and have submitted the Contributor License Agreement
• I have made this pull request to the master branch
• I have run all the unit tests using bundle exec rake
• I have run CF Acceptance Tests on bosh lite

[#118970125]

[cfdreddbot]

Hey fraenkel!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/118975023

The labels on this github issue will be updated when the story is started.

[rizwanreza]

Looks like this pull request was merged already, but not closed.