Per branch yum repo

[Metallion]

I set up the rpmbuild script to organize yum repositories based on branch to make it much easier to keep track of them and clean up old ones that are no longer needed.

Check here for an example of how this organizes yum repos: https://ci.openvdc.org/repos/per-branch-yum-repo/

Full list of changes:

• Per branch yum repos
• Removed build requirements from docker file and run yum-builddep on the spec file instead. It's better to write the build requirements only in the spec file and rely on that being correct.
• Improved path resolution in the rpmbuild script. It can now be run from any directory and no longer relies on the openvdc root folder being the current working directory.
• Renamed build stage in the CI to rpmbuild. This makes it more clear what it's doing.
• Moved rpmbuild stage after the unit tests stage. No need to build packages is the unit tests don't even pass.
• Removed the rpm install test stage. Installing the RPMs and running systemctl is not a test. Even if you run systemctl status afterwards like the script was doing, you will not catch a failed startup since it hasn't had enough time to fail yet. Instead we should write a proper acceptance test that calls the CLI and checks if OpenVDC is effectively working. (Which is my next task) An acceptance test like that will also catch broken RPM packages.