During development of a new distro, we need to test composer against
nightly or beta repositories, but we cannot ship composer itself
with the nightly repository information hardcoded in. At the same
time, we want to distinguish between the system repositories of the
host and the repositories we use to generate images (the host may not
use the same distro/version/architecture as the target, and it may
include custom repositories that the target should not).
We therefore ship per distro repository information that can be
overriden (typically in testing) by dropping files in /etc.
For now use the latest nightlies for RHEL-8.2, we may want to
replace these with the official mirrors for GA eventually.
Signed-off-by: Tom Gundersen <teg@jklm.no>
