Replace FPM Cookery with RPM spec files for third party repo

[Metallion]

Problem

In #406 we removed the FPM Cookery recipes for OpenVNet's RPM packages with plain RPM spec files. The OpenVNet third party repository is still using FPM cookery though. This should be retired.

Solution

• Rewrite the FPM Cookery recipes for the third party repository in plain RPM spec files.
• Update the build script to work with the new spec files.

The following command should build the RPMs from scratch when run in the OpenVNet root directory.

make build-rpm-third-party