missing kvm plug for nova-compute and virsh

[Dmitrii Shcherbakov]

Due to https://bugs.launchpad.net/snapd/+bug/1942640 even in devmode access to `/dev/kvm` is prohibited for applications that do not have a `kvm` plug.

It is currently present for the libvirtd application but not nova-compute or virsh, however, this may result in errors like this:

/var/snap/microstack/common/log/nova.log:2021-09-01 09:35:49.170 551126 ERROR nova.compute.manager [req-0f57efdb-5fe3-4e7c-97e2-f375aed6ea07 4a1589a2e37041a09765d67ad7a409ff 40f0600238f3409dbfa2f9dd6cb3e4ce - default default] [instance: de640782-f5c3-4c94-9232-345024036a5a] Failed to build and run instance: libvirt.libvirtError: unsupported configuration: Emulator '/snap/microstack/234/usr/bin/qemu-system-x86_64' does not support virt type 'kvm'

# Not OK.
$ sudo snap run --shell microstack.nova-compute
root@node-hagecius:/home/ubuntu/src/microstack# virt-host-validate
  QEMU: Checking for hardware virtualization : PASS
  QEMU: Checking if device /dev/kvm exists : FAIL (Check that the 'kvm-intel' or 'kvm-amd' modules are loaded & the BIOS has enabled virtualization)
  QEMU: Checking if device /dev/vhost-net exists : PASS
  QEMU: Checking if device /dev/net/tun exists : PASS
  QEMU: Checking for cgroup 'cpu' controller support : PASS
  QEMU: Checking for cgroup 'cpuacct' controller support : PASS
  QEMU: Checking for cgroup 'cpuset' controller support : PASS
  QEMU: Checking for cgroup 'memory' controller support : PASS
  QEMU: Checking for cgroup 'devices' controller support : PASS
  QEMU: Checking for cgroup 'blkio' controller support : PASS
  QEMU: Checking for device assignment IOMMU support : PASS
  QEMU: Checking if IOMMU is enabled by kernel : PASS
  QEMU: Checking for secure guest support : WARN (Unknown if this platform has Secure Guest support)

# Not OK: EPERM.
root@node-hagecius:/home/ubuntu/src/microstack# cat /dev/kvm
cat: /dev/kvm: Operation not permitted

# Not OK.
$ sudo snap run --shell microstack.virsh
root@node-hagecius:/home/ubuntu/src/microstack# virt-host-validate
  QEMU: Checking for hardware virtualization : PASS
  QEMU: Checking if device /dev/kvm exists : FAIL (Check that the 'kvm-intel' or 'kvm-amd' modules are loaded & the BIOS has enabled virtualization)
  QEMU: Checking if device /dev/vhost-net exists : PASS
  QEMU: Checking if device /dev/net/tun exists : PASS
  QEMU: Checking for cgroup 'cpu' controller support : PASS
  QEMU: Checking for cgroup 'cpuacct' controller support : PASS
  QEMU: Checking for cgroup 'cpuset' controller support : PASS
  QEMU: Checking for cgroup 'memory' controller support : PASS
  QEMU: Checking for cgroup 'devices' controller support : PASS
  QEMU: Checking for cgroup 'blkio' controller support : PASS
  QEMU: Checking for device assignment IOMMU support : PASS
  QEMU: Checking if IOMMU is enabled by kernel : PASS
  QEMU: Checking for secure guest support : WARN (Unknown if this platform has Secure Guest support)

# Not OK: EPERM.
root@node-hagecius:/home/ubuntu/src/microstack# cat /dev/kvm
cat: /dev/kvm: Operation not permitted

# OK
$ sudo snap run --shell microstack.libvirtd
root@node-hagecius:/home/ubuntu/src/microstack# virt-host-validate
  QEMU: Checking for hardware virtualization : PASS
  QEMU: Checking if device /dev/kvm exists : PASS
  QEMU: Checking if device /dev/kvm is accessible : PASS
  QEMU: Checking if device /dev/vhost-net exists : PASS
  QEMU: Checking if device /dev/net/tun exists : PASS
  QEMU: Checking for cgroup 'cpu' controller support : PASS
  QEMU: Checking for cgroup 'cpuacct' controller support : PASS
  QEMU: Checking for cgroup 'cpuset' controller support : PASS
  QEMU: Checking for cgroup 'memory' controller support : PASS
  QEMU: Checking for cgroup 'devices' controller support : PASS
  QEMU: Checking for cgroup 'blkio' controller support : PASS
  QEMU: Checking for device assignment IOMMU support : PASS
  QEMU: Checking if IOMMU is enabled by kernel : PASS
  QEMU: Checking for secure guest support : WARN (Unknown if this platform has Secure Guest support)

# OK, EPERM not received.
root@node-hagecius:/home/ubuntu/src/microstack# cat /dev/kvm
cat: /dev/kvm: Invalid argument