pci-passthrough-whitelist to allow regexps

From Xenial and on, udev renames interfaces to predictable names depending on the physical slot used in the node it runs on.

Such interface names can be: eno1, eno2, enp131s0f0, enp131s0f1, ...

We have run into the situation where multiple "nova-compute-vnf" units have different interfaces attached to physnet2 because of the naming conventions. Workaround has been to allow regular expressions to parse the devname. See sample below.

$ juju config nova-compute-vnf pci-passthrough-whitelist
'[{"devname": "eno2", "physical_network": "physnet1"}, {"devname": "enp(131|216)s0f1",
  "physical_network": "physnet2"}]'

$ sudo egrep pci /etc/nova/nova.conf
pci_passthrough_whitelist = [{"devname": "eno2", "physical_network": "physnet1"}, {"devname": "enp131s0f1", "physical_network": "physnet2"}]

https://docs.openstack.org/nova/queens/configuration/config.html#pci.passthrough_whitelist

I will send a proposal to solve this shortly.