Comment 7 for bug 1533729

Reviewed: https://review.fuel-infra.org/16490
Submitter: Vitaly Sedelnik <email address hidden>
Branch: openstack-ci/fuel-7.0/2015.1.0

Commit: 63e14f24287f26ed6d5a84eb296a04685730ff59
Author: Zane Bitter <email address hidden>
Date: Wed Jan 27 13:48:51 2016

Load template files only from their known source

Modify get_class to ensure that user-defined resources cannot result in
reads from the local filesystem. Only resources defined by the operator
in the global environment should read local files.

To make this work, this patch also adds a separate
get_class_to_instantiate() method to the Environment.

We were previously using get_class for two different purposes - to get a
resource plugin on which we could perform introspection to obtain the
properties and attributes schema, and to get a resource plugin we could
instantiate to create a Resource object. These are both the same except in
the case of a TemplateResource, where having two different use cases for
the same piece of code was adding considerable extra complexity. Combining
the use cases in this way also made the error handling confusing (leading
to bug 1518458).

This change separates out the two cases.

Change-Id: I845e7d23c73242a4a4c9c40599690ab705c75caa
Closes-Bug: #1533729