Code review comment for lp:~jamesodhunt/ubuntu/wily/ubuntu-core-upgrader/call-upgrader-directly

I put some python code comments inline, I am not sure about the approach to test the python object and the executable in two different code paths. I think it would be preferable to convert the call_upgrader_object to use the in-tree binary to avoid having two code paths. Once the code calls a external executable (the bin/ubuntu-core-upgrader from this source tree) it will be trivial to convert to call a different one once the need arises (i.e. once there is a external one that needs testing).

So instead of call_upgrader_{object,command} maybe something like:
"""
def call_upgrader(command_file, root_dir):
    pyroot = os.path.normpath(os.path.join(os.path.dirname(__file__), ".."))
    env = copy.copy(os.environ)
    env["PYTHONPATH"] = pyroot
    subprocess.check_call(
        [os.path.join(pyroot, "bin", "ubuntu-core-upgrade"),
         '--root-dir', root_dir,
         '--debug', '1',
         # don't delete the archive and command files.
         # The tests clean up after themselves so they will get removed then,
         # but useful to have them around to diagnose test failures.
         '--leave-files',
         command_file],
    env=env)
"""