Cannot specify Mac address for bridge

My hosting provider requires me to use Mac addresses provided by themselves so that their network will accept my ethernet packets. They also require a strict proscribed static IP allocation. Without the correct Mac address, my VM cannot send/receive data to/from the network.

I am running uvt-kvm like this:

uvt-kvm create --password changeme --memory 4096 --disk 40 --cpu 2 --bridge br0 --packages openssh-server,mosh,git,vim,puppet,screen,ufw --meta-data /tmp/22720db9-abaf-4ab4-a602-fe16e76715bd-meta-data my-vm123 release=bionic

With a meta-data file that looks like:

instance-id: 22720db9-abaf-4ab4-a602-fe16e76715bd
local-hostname: my-vm123
network-interfaces: |
  iface ens3 inet static
  hwaddress ether 06:00:00:42:9b:44
  address 54.36.67.139
  network 54.36.67.139
  netmask 255.255.255.255
  broadcast 5.196.205.132
  gateway 91.121.89.254
  dns-nameservers 213.186.33.99
  dns-search mydomain.com

However, the problem that I have when using the `--bridge br0` is that the Mac address for the vnet adapter created for that bridge is seemingly randomly assigned.

I attach a patch that adds a `--mac` parameter to uvt-kvm which allows the user to specify the Mac address for the interface. I have tested it here and it sets the Mac correctly, both when using a bridge and when not using a bridge.

With the patch I can execute uvt-kvm like:

uvt-kvm create --password changeme --memory 4096 --disk 40 --cpu 2 --bridge br0 --mac 06:00:00:42:9b:44 --packages openssh-server,mosh,git,vim,puppet,screen,ufw --meta-data /tmp/22720db9-abaf-4ab4-a602-fe16e76715bd-meta-data my-vm123 release=bionic