Code simplification suggestions

It may not be necessary to render_config upon charm install, as config-changed hook which also calls render_config is to follow immediately after an install hook. Suggest removing:

    self.framework.observe(self.on.install, self.render_config)

Setting the initiator_name in _iscsi_initiator() could be simplified to:

        initiator_name = initiators_dict.get(hostname, subprocess.getoutput('/sbin/iscsi-iname'))
        if hostname not in initiator_dict:
            logging.warning('The hostname was not found in the initiator dictionary!' +
                            'The random iqn %s will be used for %s',
                            initiator_name, hostname)

Functional test bundles could be set up with base.yaml and symlinks from focal.yaml and bionic.yaml along with moving "series: <distro>" to overlay templates, and charm_name variable should be lower-cased in the overlay templates. i.e. a suggested overlay template focal.yaml.j2:

series: focal
applications:
  {{ charm_name }}:
    charm: {{ CHARM_BUILD_DIR }}/{{ charm_name }}.charm