sunbeam configure allows invalid interface name

[Andre Ruiz]

When installing sunbeam I have given an non-existing interface name as the OVN network interface in the manifest file, and later I got the error:

09:46:29 > Applying local hypervisor settings ... setting hypervisor configuration for sunbeam11.mydomain
09:46:33 An unexpected error has occurred. Please run 'sunbeam inspect' to generate an inspection report.
09:46:33 Error: {'return-code': 1, 'stderr': 'error: snap "openstack-hypervisor" has no "network.external-nic" configuration\n option\nerror: cannot perform the following tasks:\n- Run configure hook of "openstack-hypervisor" snap (run hook "configure": \n-----\nTraceback (most recent call last):\n File "/snap/openstack-hypervisor/150/snap/hooks/configure", line 9, in <module>\n sys.exit(configure(Snap()))\n File "/snap/openstack-hypervisor/150/lib/python3.10/site-packages/openstack_hypervisor/hooks.py", line 1287, in configure\n _configure_ovn_external_networking(snap)\n File "/snap/openstack-hypervisor/150/lib/python3.10/site-packages/openstack_hypervisor/hooks.py", line 798, in _configure_ovn_external_networking\n _ensure_link_up(external_nic)\n File "/snap/openstack-hypervisor/150/lib/python3.10/site-packages/openstack_hypervisor/hooks.py", line 851, in _ensure_link_up\n dev = ipr.link_lookup(ifname=interface)[0]\nIndexError: list index out of range\n-----)\nUncaught SnapError in charm code: Snap: \'openstack-hypervisor\'; command [\'snap\', \'set\', \'openstack-hypervisor\', \'-t\', \'network.external-nic="bond0.1001"\'] failed with output = \'\'\nUse `juju debug-log` to see the full traceback.\n'}
09:46:33 DEBUG: execute return code is 1

Seems like this should be caught at the beginning (a check for the interface name should be done when processing the manifest or interactively asking for the interface name) to avoid this error much later in the process.