add copr as an alternative to building on lxc or docker

[tpokorra]

define a machine with credentials for copr.

use the copr api: https://copr.fedorainfracloud.org/api/

• copr has fast build machines
• copr hosts the repo and provides good download
• I could build complex projects with multiple packages depending on each other in the right order on copr
• LBS would check when a package has finished, and then start building the next package
• could build packages in parallel, that don't depend on each other
• LBS creates the SRPM, and uploads that to copr

[tpokorra]

to make it easier, this works only if rpmbuild is available on the lbs server, so that we can build the src.rpm file and use it for copr

to make it easier, the tarball is expected in the git repository. no support at the start for config.yml to reference the tarball.

use a different rpmbuild directory for each package (under user uwsgi)

[tpokorra]

TODO: allow parallel builds of packages that don't depend on each other