No error's reported if heat stack creation/update fails

Adds error status reason text to exception message that is raised
when Heat stack create/update fails

Also disables stack rollback for consistency (otherwise if error happens during
stack creation it silently disappears and no reason provided)

Change-Id: Ia4366cba486e9ce4c5ae35ecb3e042bbf5f7ef3d
Closes-Bug: #1369722