It was a functionality available in charm helpers. It is implemented in
a similar way:
* Get the current series from the `keystone` machine
* Get the OS version from `get_current_os_versions`
* Try to find the built string in `OPENSTACK_RELEASES_PAIRS`
It is thus possible to compare release pairs as it returns integers.
Bring over only those utilities required to run network_setup.py from
openstack-mojo-specs. These utilities have been generalized and python3
configured. Use libjuju whenever possible and pre-deprecate anything
else.
Add addition functions to the model.
