build: create poni/version.py by default + some cleanups
template: make render_name's escaping behave like cheetah's

render_name used to handle double escapes (escaping escapes) but left the
escapes intact in the rendered output.  Removed the escapes from output and
made it behave like Cheetah which handles the single escapes in front of a
dollar-sign, escapes can't be escaped.

Also added a few test cases to make sure render_name and render_cheetah
behave identically.
Merge pull request #30 from saaros/template

More render_name fixes
libvirt: make hypervisor configurable but only support kvm for now
libvirt: preliminary support for lxc targets and btrfs storage

NOTE: btrfs volumes require a patched libvirt, see
https://www.redhat.com/archives/libvir-list/2013-September/msg00058.html