Comment 16 for bug 1828259

Adding neutron-openvswitch and nova-compute charms because:

1) nova-compute charm needs to make sure neutron-l3-agent is not accidentally purged before python3-packages are installed by neutron-openvswitch;

2) neutron-openvswitch needs to be notified about the primary charm upgrade.

If nova-compute is not modified and only neutron-openvswitch is then there will be a period of time after purge and before config-changed when Neutron networking will be completely gone as a result of removal of neutron-l3-agent.