Previously, this code was not checking for the proper environment
variable for an element's installtype. There was a line replacing '-'
with '_' as is required, but that value was not actually used when
searching for the environment variable.
Change-Id: I0bbd56969188389db81844d9276269464870f776
Instead of doing the work in the image of parsing through the element's
package-install declarations, we can squash it on hostside, where we
have both YAML and JSON available to us, and then emit a single
pre-processed file into the target to be used later.
Change-Id: I3f182aa3aae0a79b2f3ea4e66c1878ad12878b0a
