This change contains refactoring of the template validation and loading,
in order to allow different validators and loaders for execute_mistral
action in versions 1 and 2.
* template_versions.py contains all supported versions, including their
validators and loaders (and in the future - functions like get_attr())
* template_version_factory.py allows getting the right template version
instance
* validators and loaders are retrieved only from the template-version
instance, and are no longer created directly
* All content validators and loaders were moved under v1 and v2 packages
In addition, the structure of execute_mistral has changed, so now all
the input parameters of the workflow must reside under an 'input' section.
Change-Id: I8eebc79b0885eab9c013fafdc17ae8378c7bcedf
4576523641