User defined system configuration

[bmeneg]

This issue is a "re-open" of the issue #1601 that I closed by mistake.

When testing something like the kernel or even userspace with hardware dependent features, it's a good thing to define a set of system configurations with a single name, for instance:

AMD__ROME:
CPU family=23
CPU model=49

MEMORY_MIN_64G
SYSTEM memory >= 64G

NOGSS:
SYSTEM name != "%gss%"

The first line would be the host-filter name, while the other lines would then be the actual system configuration requirements.
Some of these might make sense to all runners, but when using Beaker for bare-metal reservation and testing this feature is really important and a must, even more the idea of accepting some "regular expressions" for generalization.

On Beaker, all host-filters were just XML's tags dropped on the final recipe XML in the system requirements section, but on TMT/FMF it could follow another format for sure..