Fix for bridged networks.
Fix for bridged networks.

Need to make domain attribute optional, as not used for bridge
Disabling forwarding for bridged networks
Ensure that parsing existing network doesn't fail due to lack
of domain attribute

dmacvicar/terraform-provider-libvirt,deasmi/terraform-provider-libvirt,dmacvicar/terraform-provider-libvirt,deasmi/terraform-provider-libvirt,flavio/terraform-provider-libvirt,dmacvicar/terraform-provider-libvirt,deasmi/terraform-provider-libvirt