Add heat parameter for all of config_volume images

Add heat parameter for all of config_volume images

This commit consistently defines a heat template parameter in the form
of DockerXXXConfigImage where XXX represents the name of the
config_volume that is used by docker-puppet.

The goal is to mitigate hard to debug errors where the templates would
set different defaults for the image docker-puppet.py uses to run, for
the same config_volume name.

This fixes a couple of inconsistencies on the way.

Change-Id: I212020a76622a03521385a6cae4ce73e51ce5b6b
Closes-Bug: #1699791