cloud_libvirt: fix python 2.6 compatibility with re.split
cloud_libvirt: fix python 2.6 compatibility with re.split

Travis noticed (after merging Travis configuration fixes on top of the
libvirt changes) that `re.split` doesn't take a `flags` argument on Python
2.6.  Fix this by pre-compiling the expression.

ohmu/poni,ohmu/poni