[GH-2706] Update ruby-libvirt dependency to 0.5

Also removed guard related to JRuby since the important part is opting
into lib-virt
[rackspace|compute_v2] adds virtual interfaces support
Merge branch 'master' of github.com:fog/fog into virtual_interfaces
Merge pull request #2728 from rackspace/virtual_interfaces

[rackspace|compute_v2] add virtual interface support.
Merge pull request #2720 from fog/2706_bump_libvirt

[GH-2706] Update ruby-libvirt dependency to 0.5