This mirrors the change made for providers, so that default values can
be inserted into the config by the backend implementation. This is only
the interface and method name changes, it does not yet add any default
values.
This PR improves the error handling so we can provide better feedback about any service discovery errors that occured.
Additionally it adds logic to test for specific versions when discovering a service using `service.vN`. This will enable more informational errors which can indicate any version incompatibilities.
In order to support free organizations, we need a way to load the `remote` backend and then, depending on the used offering/plan, enable or disable remote operations.
In other words, we should be able to dynamically fall back to the `local` backend if needed, after first configuring the `remote` backend.
To make this works we need to change the way this was done previously when the env var `TF_FORCE_LOCAL_BACKEND` was set. The clear difference of course being that the env var would be available on startup, while the used offering/plan is only known after being able to connect to TFE.
This work was done against APIs that were already changed in the branch
before work began, and so it doesn't apply to the v0.12 development work.
To allow v0.12 to merge down to master, we'll revert this work out for now
and then re-introduce equivalent functionality in later commits that works
against the new APIs.
Alisdair McDiarmid