This augments backend-config to also accept key=value pairs.
This should make Terraform easier to script rather than having to
generate a JSON file.
You must still specify the backend type as a minimal amount in
configurations, example:
```
terraform { backend "consul" {} }
```
This is required because Terraform needs to be able to detect the
_absense_ of that value for unsetting, if that is necessary at some
point.
This adds a "lock" config (default true) to allow users to optionally
disable state locking with Consul. This is necessary if the token given
doesn't have session permission and is necessary for backwards
compatibility.
Mitchell Hashimoto