Bug fix #463: Allow add networks with non-ASCII characters to template and guest

Kimchi uses unicode internally but libvirt stores its data encoded with
utf-8. So we also need to encode the given value to utf-8 to compare it
properly to libvirt results.
Also add test cases to cover this scenario.

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>