Vagrant group in comps

[Josef Stribny]

Hi all,

I would like to introduce a new @vagrant group that should pull in vagrant
with vagrant-libvirt plugin (at the very least) since libvirt might be
the preferred virtualization when used with Vagrant on Fedora and I would
like to encourage users to use the packaged plugin.

Also, we set libvirt as a default provider in the Fedora package and I think
it would be nicer to recommend "install Vagrant group" instead of
"install vagrant-libvirt package".

What do you think? Is it reasonable or unnecessary?

(Btw. this is connected with the new Fedora 22 Vagrant feature[0])

Regards
Josef

[0] https://fedoraproject.org/wiki/Changes/Vagrant