Remove hardwired url patterns from inputs
Override repositories with environment variables
Extract variables
Rename variables

The same environment variables could be used for both deb and rpm packages:

PKG_REPO_LOCATION
SRC_REPO_LOCATION
Fix bad variable name
Templated debian preferences

If the repo location is an URL, the debian preference file need to refer
to the hostname.
Merge pull request #316 from matelakat/install-from-url

Enable URL based installation