add_source fails: add-apt-repository not found

[Merlijn Sebrechts]

From the topbeat charm:

Traceback (most recent call last):
  File "hooks/install", line 19, in <module>
    main()
  File "/var/lib/juju/agents/unit-topbeat-0/.venv/lib/python3.4/site-packages/charms/reactive/__init__.py", line 73, in main
    bus.dispatch()
  File "/var/lib/juju/agents/unit-topbeat-0/.venv/lib/python3.4/site-packages/charms/reactive/bus.py", line 421, in dispatch
    _invoke(other_handlers)
  File "/var/lib/juju/agents/unit-topbeat-0/.venv/lib/python3.4/site-packages/charms/reactive/bus.py", line 404, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-topbeat-0/.venv/lib/python3.4/site-packages/charms/reactive/bus.py", line 280, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-topbeat-0/charm/reactive/beats_base.py", line 12, in install_beats_repo
    configure_sources(update=True)
  File "/var/lib/juju/agents/unit-topbeat-0/.venv/lib/python3.4/site-packages/charmhelpers/fetch/__init__.py", line 363, in configure_sources
    add_source(source, key)
  File "/var/lib/juju/agents/unit-topbeat-0/.venv/lib/python3.4/site-packages/charmhelpers/fetch/__init__.py", line 289, in add_source
    subprocess.check_call(['add-apt-repository', '--yes', source])
  File "/usr/lib/python3.4/subprocess.py", line 556, in check_call
    retcode = call(*popenargs, **kwargs)
  File "/usr/lib/python3.4/subprocess.py", line 537, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.4/subprocess.py", line 859, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.4/subprocess.py", line 1457, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'add-apt-repository'

add-apt-repository is not present on all Ubuntu instances. Some don't have it by default.

[Stuart Bishop (stub)]

bootstrap needs to ensure the relevant package is installed. I think it is software-properties-common, but I'm not sure if it is the same across all releases.