api_key or apikey

[rizumu]

In python-cloudservers api_key was used, but now it's apikey. The documentation (including shell help) doesn't match the source in a few places on change and led to some brief confusion during an upgrade.

Also the docs read:

compute = openstack.compute.Compute(USERNAME, API_KEY)

But a kwarg is expected:

compute = openstack.compute.Compute(username=USERNAME, apikey=API_KEY)