TAP device doesn't attach to bridge

[richardcase]

What happened:
When creating a microvm with a tap device it doesn't attach to the linux bridge.

What did you expect to happen:
I expect the microvm to be attached to the bridge.

How to reproduce it:

1. Start flintlock with the patent device set to a bridge --parent-iface virbr0
2. Create a VM like this:

fl microvm create --host 127.0.0.1:9090 --name fctest --metadata-hostname fctest --network-interface eth1:tap  --metadata-ssh-key-file ~/.ssh/id_ed25519.pub --memory 4096 --root-image ghcr.io/weaveworks-liquidmetal/flintlock-ubuntu-perftest:7987e91 --vcpu 2

A new tap interface should be created and attached to the virbr0. But this isn't happening:

➜ virsh net-info default
Name:           default
UUID:           f13f5027-0de7-477d-822e-35245ba26abc
Active:         yes
Persistent:     yes
Autostart:      yes
Bridge:         virbr0

➜ brctl show virbr0
bridge name     bridge id               STP enabled     interfaces
virbr0          8000.5254006069f3       yes             

➜ virsh net-dhcp-leases default
 Expiry Time           MAC address         Protocol   IP address          Hostname   Client ID or DUID
-----------------------------------------------------------------------------------------------------------------------------------------------

Environment:

• flintlock version: v0.1.0 (latest main)