hook failures for unsupported/containers

[Haw Loeung]

Hi,

On unsupported/containers, the charm fails as follows:

2018-11-12 00:26:24 INFO juju-log OS container detected, livepatch is not needed
2018-11-12 00:26:24 INFO juju-log Invoking reactive handler: reactive/canonical_livepatch.py:249:configure_nagios
2018-11-12 00:26:24 INFO juju-log Setting charm primary status False
2018-11-12 00:26:24 ERROR juju-log Hook error:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-canonical-livepatch-1/.venv/lib/python3.6/site-packages/charms/reactive/__init__.py", line 73, in main
    bus.dispatch(restricted=restricted_mode)
  File "/var/lib/juju/agents/unit-canonical-livepatch-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 390, in dispatch
    _invoke(other_handlers)
  File "/var/lib/juju/agents/unit-canonical-livepatch-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 359, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-canonical-livepatch-1/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 181, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-canonical-livepatch-1/charm/reactive/canonical_livepatch.py", line 270, in configure_nagios
    write_status_to_disk()
  File "/var/lib/juju/agents/unit-canonical-livepatch-1/charm/reactive/canonical_livepatch.py", line 71, in write_status_to_disk
    current_status = get_livepatch_status()
  File "/var/lib/juju/agents/unit-canonical-livepatch-1/charm/reactive/canonical_livepatch.py", line 59, in get_livepatch_status
    livepatch_status = check_output(cmd, universal_newlines=True)
  File "/usr/lib/python3.6/subprocess.py", line 336, in check_output
    **kwargs).stdout
  File "/usr/lib/python3.6/subprocess.py", line 403, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/usr/lib/python3.6/subprocess.py", line 709, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.6/subprocess.py", line 1344, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: '/snap/bin/canonical-livepatch': '/snap/bin/canonical-livepatch'

I think we just need to have an 'unsupported' flag and skip configure_nagios() on that.

[Haw Loeung (hloeung)]

Related, /etc/cron.d/check_canonical-livepatch gets shipped out by configure_nagios() and causes cron spam:

Date: Sun, 11 Nov 2018 17:17:01 +0000 (UTC)
From: Cron Daemon <email address hidden>
To: <email address hidden>
Subject: Cron <root@kimura> /snap/bin/canonical-livepatch status >
        /var/lib/nagios/canonical-livepatch-status.txt

/bin/sh: 1: /snap/bin/canonical-livepatch: not found