Import RPM build dependencies from CentOS and EPEL

Build dependencies from CentOS and EPEL

The source RPMs provided by the Xenserver project do not include many needed build dependencies from CentOS and EPEL.

One can guess that Citrix has internal frozen repositories for those packages and does not communicate about their contents (we can mostly infer it from RPM build dependencies), nor says what exact versions of the packages are used (we have to guess). It looks like they stick to a given version of CentOS (e.g. 7.2) for some time, maybe with a few exceptions.

Xenserver 7.6 still relied mostly on the old CentOS 7.2 so we can use the frozen CentOS 7.2 repositories from vault.centos.org (version 8 should bring fresh air with more recent packages from CentOS). However EPEL packages (they are only a few, thankfully) are not frozen so there's a risk we'd use a version that is "too" recent and brings incompatibilities.

Add the missing dependencies to Koji

Hunting the missing dependencies one by one based on build errors would be very time-consuming and frustrating, so we figured out a way to script most of it.