Initial RHEV network implementation

There is not much in this patch, it adds only network listing.
RHEV networking is quite different from cloud providers like EC2.
A user is allowed to create a VNIC(s) for a VM, then by associating
these VNICs with networks she specifies to which network the VM
belongs to.

This patch requires rbovirt with commit b832f8ad48c333207dbfa7656420f7e2724bcb28
(you can build from actual https://github.com/abenari/rbovirt master branch)