Expose all versions of Ironic API

In the observable future new versions of the Ironic
API will appear. That's why it's reasonable to expose
the endpoint that will provide access to all versions
of the API.

Closes-Bug: #1229780
Change-Id: I4ec2b45688da3fa6c0d43e8be60885774cfbffd6
Merge "Expose all versions of Ironic API"