Remove testscenarios load_tests

A load_tests call sneaked in test_provider_template, but it's become
useless since we switch to a base heat test class that provides what's
needed.

Change-Id: Ie5665cbbafb46a7ed63ada37a3f4aa5c74cdb8b6
Add missing test coverage for XMLResponseSerializer

Currently we have no direct coverage of this, so add some tests
prior to refactoring in a subsequent patch.

Change-Id: I20242e60b84f9265cdc7afef2deabee8235e287c
Related-Bug: #1291079
Refactor to separate serializers from wsgi controller

Remove the serializers from heat.common.wsgi, so we break the
circular import which happens if you want to import
heat.api.aws.exceptions to do a determination based on exception
type, which is required to avoid the faultwrap exception disguise
which is not applicable to the CFN API.

Partial-Bug: #1291079

Change-Id: I7498d78f8ec6098b28fb183eaaa04aa81fced3eb
Don't disguise CFN API exceptions

The exception disguise wrapper is for the native API which uses
the faultwrap filter to process the response. For HeatAPIException
subclasses (which are only raised by the CFN/CW API's) we need to
raise the unwrapped exception or the client sees a 500 response.

Change-Id: Iebfbc76d5cb26aa9ee61c5192d7fecc596aa83b9
Closes-Bug: #1291079
Merge "Remove testscenarios load_tests"