NTP upgrade-charm failed on start hook

[Adam Dyess]

upgrading from ntp-35 to ntp-45, failed on some units because charmhelpers package was not updated to the version available in the charm's wheelhouse.

$ juju run -u ntp/127 hooks/start
active
active
ntp.service is not a native service, redirecting to systemd-sysv-install
Executing /lib/systemd/systemd-sysv-install enable ntp
Traceback (most recent call last):
  File "hooks/start", line 22, in <module>
    main()
  File "/var/lib/juju/agents/unit-ntp-127/.venv/lib/python3.5/site-packages/charms/reactive/__init__.py", line 73, in main
    bus.dispatch(restricted=restricted_mode)
  File "/var/lib/juju/agents/unit-ntp-127/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 390, in dispatch
    _invoke(other_handlers)
  File "/var/lib/juju/agents/unit-ntp-127/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 359, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-ntp-127/.venv/lib/python3.5/site-packages/charms/reactive/bus.py", line 181, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-ntp-127/charm/reactive/ntp.py", line 295, in update_nrpe_config
    max_check_attempts=hookenv.config('max_check_attempts'),
  File "/var/lib/juju/agents/unit-ntp-127/.venv/lib/python3.5/site-packages/charmhelpers/contrib/charmsupport/nrpe.py", line 276, in add_check
    self.checks.append(Check(*args, **kwargs))
TypeError: __init__() got an unexpected keyword argument 'max_check_attempts'

$ juju run -u ntp/127 '../.venv/bin/pip freeze'
asn1crypto==0.22.0
blinker==1.3
certifi==2015.11.20.1
chardet==3.0.4
charmhelpers==0.19.16

$ juju run -u ntp/127 'ls wheelhouse/charmhelpers*'
wheelhouse/charmhelpers-0.20.20.tar.gz

[Drew Freiberger (afreiberger)]

This "should" be fixed in layer-basic.

If this charm could be re-built with the latest layer-basic and tested for this error again, that would be helpful in determining if the bug still exists in layer-basic.

https://github.com/juju-solutions/layer-basic/pull/105