render stack parameters in the correct order

Parameters in a heat template are now rendered in the order specified
in the "ParameterGroups" section. If this section is not available then
they are rendered unordered.

Change-Id: I3367b42c4c3037666b705cebf9cf67ccf0ce4fce
Closes-Bug: 1364567
Merge "render stack parameters in the correct order"