Comment 6 for bug 1799500

The original failure:

2018-11-28 21:31:43 INFO juju-log Registered config file: /etc/apache2/ports.conf
2018-11-28 21:31:44 DEBUG install Traceback (most recent call last):
2018-11-28 21:31:44 DEBUG install File "/var/lib/juju/agents/unit-openstack-dashboard-0/charm/hooks/install.real", line 109, in <module>
2018-11-28 21:31:44 DEBUG install CONFIGS = register_configs()
2018-11-28 21:31:44 DEBUG install File "/var/lib/juju/agents/unit-openstack-dashboard-0/charm/hooks/horizon_utils.py", line 199, in register_configs
2018-11-28 21:31:44 DEBUG install if os.path.isdir(APACHE_CONF_DIR) and cmp_pkgrevno('apache2', '2.4') >= 0:
2018-11-28 21:31:44 DEBUG install File "/var/lib/juju/agents/unit-openstack-dashboard-0/charm/charmhelpers/core/host_factory/ubuntu.py", line 91, in cmp_pkgrevno