(gh-552) Add support for vagrant_libvirt

Currently vagrand backend support is limited to virtualbox,
vmware_workstation and fusion. Vagrant offers a non-official
libvirt backend through the vagrant-libvirt[1] plugin.
This commit aims to add support for vagrant_libvirt.

[1] https://github.com/pradels/vagrant-libvirt
Merge pull request #551 from Mylezeem/support_vagrant_libvirt

(GH-552) Hypervisor: Add support for vagrant_libvirt
(QENG-299) Added support for EOS
(QENG-299) applied review feedback

two specific things were done here: removal of unnecessary pe_dir
setting in spec tests, and changing HEREDOC usage to string array
join calls for better readability
Merge pull request #553 from kevpl/qeng299_eos_added

(QENG-299) Added support for EOS
(QENG-1266) added cumulus support to beaker
(QENG-1266) added in review feedback