Add trivial way to drop RPMs (or even tarballs) into local/

[cgwalters]

Let's have a default model where a developer or test process can do:

# mkdir -p local-overrides
# cp /path/to/kernel.rpm local-overrides

And if we find any RPMs in there we automatically run createrepo_c and add it to the config. One thing this will then hit is: rpm-software-management/libdnf#149
Which...hacking around would be very painful.

[cgwalters]

And to generalize this, might as well support local-overrides/foo.tar.gz which we unpack and apply on top.

[dustymabe]

yeah I do this today with a local.repo file and a localrepo directory.

this reminded me about an RFE I asked you about a while ago so I just opened it: coreos/rpm-ostree#1572

I'm a big 👍 for something like this.