Ensuring environment data is passed to heat template validate

 - environment data was being passed to heat API on stack create,
   but not stack validate - meaning that templates that referenced
   environment files were not validating correctly

 - heat client does not support URLs for environment files - we will
   need to do this client side before POSTing back to horizon. future
   patch

Partial-Bug: #1322258

Change-Id: I40982b777abaec743ed6cbc527008522a619e817
Merge "Ensuring environment data is passed to heat template validate"