Add optional args arg back to do_list

Without this change "heat list" does not work.

Change-Id: Ie0bc4d0964fcb9d7a5e3271b739f053eb1c701fd
Closes-Bug: #1278178
Fixes environment file using correct YAML format

An internal unexpected exception is raised while create a stack with an
environment file which only has string content. We should handle the case
and raise the correct error message such as "environment file is not Yaml
format".

Change-Id: I4e124db6a8dca9cf811f151ae95058cdaae16a01
Closes-Bug: #1273974
Add support for software config resources

SoftwareConfig lacks update methods as it is immutable.

Implements: blueprint hot-software-config-rest

Change-Id: I1d05433303c182f03d21378fd66af4f589b7821b
Merge "Add optional args arg back to do_list"
Merge "Fixes environment file using correct YAML format"