Many apps deployed to Heroku require that multiple buildpacks be
configured in a particular order to operate correctly.
This updates the builtin Heroku provider's app resource to support
configuring buildpacks and the related documentation in the website.
Similar to config vars, externally set buildpacks will not be altered if
the config is not set.
The default stack changed from ‘cedar’ to ‘cedar-14’, so updated the
acceptance tests to reflect this.
Updating the schema makes testing easier and gives you a way to
configure the provider using env variables. It also makes the provider
more inline following the TF 0.2 approach.
cc/ @catsby if you're curious. That fixed the acceptance tests,
thought there is still one (different issue) that is still failing.
Also, it nows construct a transport instead of using the default
and setting the auth globally. TF could potentially run things
concurrently and that might go wrong.
cmorent