When making a new release that contains commits that have already been
merged onto c10s (but not build) running make release would result in an
empty changelog.
This adds the PREV environmental variable so that the hash of the
previous release can be used as the reference for creating the clog.
eg. PREV=ACTUALHASH make release
Where ACTUALHASH is the git hash of the commit used to make the previous
release. Usually this is one commit before the first commit you want to
include in this build.
Related: RHEL-40021
...turns out you can't just have a single template file, because lorax
just picks a single directory and expects all the data it needs to be
there. Sigh.
So this adds all the rest of the files, plus some Makefile machinery for
generating a tarball and updating the specfile after you've checked in
changes. See README for details.
