Description of problem:
When attempting to create a heat stack in Horizon it immediately fails with "Danger there was an error submitting the form". It seems to fail before the request reaches the heat api. The same templates work in RHOSP 13 and also via the cli in this 16.2 environment.

Version-Release number of selected component (if applicable):


How reproducible:
Consistently in this 16.2 environment

Steps to Reproduce:
1. Log in to horizon
2. Attempt to create a heat stack
3. 

Actual results:
Danger there was an error submitting the form

Expected results:
Successful stack creation

Additional info:

If this parameter (the actual url in the template is valid) is removed we're able to get past the form submission failure:

      config_file_content: {get_file: 'http://example.com/path/to/file.txt'}