postgresql failing to install on Xenial

[David Ames]

cs:postgresql is not able to install on Xenial and fails immediately on the pg_createcluster command:

unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install Error: cluster configuration already exists
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install Traceback (most recent call last):
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/var/lib/juju/agents/unit-xenial-0/charm/hooks/install", line 22, in <module>
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install main()
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/var/lib/juju/agents/unit-xenial-0/.venv/lib/python3.5/site-packages/charms/reactive/__init__.py", line 74, in main
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install bus.dispatch(restricted=restricted_mode)
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/var/lib/juju/agents/unit-xenial-0/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 390, in dispatch
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install _invoke(other_handlers)
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/var/lib/juju/agents/unit-xenial-0/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 359, in _invoke
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install handler.invoke()
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/var/lib/juju/agents/unit-xenial-0/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 181, in invoke
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install self._action(*args)
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/var/lib/juju/agents/unit-xenial-0/charm/reactive/postgresql/service.py", line 210, in create_cluster
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install postgresql.create_cluster()
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/var/lib/juju/agents/unit-xenial-0/charm/reactive/postgresql/postgresql.py", line 369, in create_cluster
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install subprocess.check_call(cmd, universal_newlines=True)
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install File "/usr/lib/python3.5/subprocess.py", line 581, in check_call
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install raise CalledProcessError(retcode, cmd)
unit-xenial-0: 18:01:29 WARNING unit.xenial/0.install subprocess.CalledProcessError: Command '['pg_createcluster', '-e', 'UTF-8', '--locale', 'C', '9.5', 'main', '--', '--data-checksums']' returned non-zero exit status 1

[Stuart Bishop (stub)]

Xenial packages don't support /etc/postgresql-common/createcluster.d configuration, so package installation created a database, and the charm can't continue because it can't tell if the existing database contains important information or not. Work around by using /etc/postgresql-common/createcluster.conf instead under xenial.