re-enable test_cli in package builds

[Scott Moser]

revision 1106 made tests in test_cli.py get skipped if there was no bin/cloud-init.

that was because package builds would fail, like:

======================================================================
ERROR: test_no_arguments_shows_error_message (unittests.test_cli.TestCLI)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/«PKGBUILDDIR»/.pybuild/pythonX.Y_3.4/build/tests/unittests/test_cli.py", line 46, in test_no_arguments_shows_error_message
    self._call_main()
  File "/«PKGBUILDDIR»/.pybuild/pythonX.Y_3.4/build/tests/unittests/test_cli.py", line 28, in _call_main
    'cli', open('bin/cloud-init'), '', ('', 'r', imp.PY_SOURCE))
FileNotFoundError: [Errno 2] No such file or directory: 'bin/cloud-init'

[Dan Watkins (oddbloke)]

Scott, the best way of handling this is probably to make bin/cloud-init a tiny wrapper around something that's part of the library (i.e. just move the vast majority of the contents to cloudinit.cli or cloudinit.main). Does that sound like a sensible approach?

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2548