Fixes #11089 - Adapt tests to Rails 4

This commit contains all changes to tests in branch
https://github.com/theforeman/foreman/pull/2055 that I found to be
retrocompatible with Rails 3. The more of these we can get in, the less
code we will have to review for Rails 4, and the more relevant it will...

Fixes #8343 - Consolidated code paths, and removed unnecessary DB calls for parent object

Fixes #11078 - Substitute find_all_by by where to comply with Rails 4

This commit takes away all instances up to this point of find_all_by to
improve Rails 4 compatibility. They are substituted by .where calls.

Fixes #10356 - changed the POST/PUT RABL template to be the same as the GET template

HTTP response code standardized to 201 on create.

Fixes #10963 - partition table can't access os ids

Refs #10720 - Use API v2 response for vm_compute_attributes

Fixes #6976 - Build default PXE menu should be POST request

Fixes #7096 - Adds STI to templates

This commit converts Ptables to be just another type of Template so it
gets the same features as ConfigTemplate. ConfigTemplate was renamed to
ProvisioningTemplate to reflect UI and the name under it's commonly known.

fixes #10720 - Adds API to get host vm attributes

This exposes an API to fetch a host's vm_compute_attributes,
such as vmware cpus and memory. It lives at a separate endpoint
because it involves a fetch for data from the compute resource,
and may have different performance characteristics than the database.

Fixes #10715 - api build_pxe_default returns non-JSON message

The fix adds a new method `render_message` for responding with a status
text.