Deploying into jammy lxds fails due to lack of /etc/fstab

[Barry Price]

Per summary, deploying into LXD containers running jammy (and/or later series?) fails with a traceback due to those containers not shipping an /etc/fstab file:

2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 Traceback (most recent call last):
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 File "/var/lib/juju/agents/unit-jammy-1/charm/hooks/config-changed", line 1236, in <module>
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 hooks.execute(sys.argv)
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 File "/var/lib/juju/agents/unit-jammy-1/charm/hooks/charmhelpers/core/hookenv.py", line 934, in execute
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 self._hooks[hook_name]()
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 File "/var/lib/juju/agents/unit-jammy-1/charm/hooks/config-changed", line 1181, in config_changed
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 configure_bind_mounts(conf, hostname)
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 File "/var/lib/juju/agents/unit-jammy-1/charm/hooks/config-changed", line 280, in configure_bind_mounts
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 update_bind_mounts(required_mounts)
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 File "/var/lib/juju/agents/unit-jammy-1/charm/hooks/config-changed", line 241, in update_bind_mounts
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 managed_mounts = get_managed_mounts()
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 File "/var/lib/juju/agents/unit-jammy-1/charm/hooks/config-changed", line 181, in get_managed_mounts
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 with open("/etc/fstab", "r") as f:
2023-07-06 08:25:25 WARNING unit.jammy/1.config-changed logger.go:60 FileNotFoundError: [Errno 2] No such file or directory: '/etc/fstab'

Options could be:

1. Explicitly state no support for containers, optionally adding code to detect a containerised deploy - and warning the operator
2. Gracefully handle the lack of an /etc/fstab and add logic to operate as expected