Added support for interface name in cloud-init, implements #559

[ivomarino]

Implements interface name specification for set-name in cloud-init, this is required to set e.g. vio0 on OpenBSD, the default value eth0 will not work there. Example:

cat bhyve-openbsd-cloud.sh
sudo vm create \
-t openbsd \
-s 4G \
-c 2 \
-m 512M \
-i openbsd-min.qcow2 \
-C -n "interface=vio0;ip=192.168.1.12/24;gateway=192.168.1.1;nameservers=192.168.1.1" \
-k /home/user/.ssh/id_rsa.pub \
openbsd-test-cloud