The module currently has a static 'required_if' statement for its
parameters that forces any of 'username' or 'activationkey' or 'token'
in case state=present; while this is generally a good idea, it can be
an extra requirements in some cases. In particular, if the system is
already registered, there is no need for credentials -- some of the
operations of the module, such as manipulating pools, can be done
perfectly without credentials.
Hence:
- change the static 'required_if' to require credentials only when
forcing the registration
- check for credentials manually when a registration is needed, i.e.
on an unregistered system; the fail message is the same as the one
shown by 'required_if'
Adapt the tests to this new situation:
- test_without_required_parameters now needs to mock an unregistered
system
- add a new version of test_without_required_parameters to test an
already registered system
- add a simple test case for only state=present usable on an already
registered system
- remove the credentials from a test case for pool attachment that
mocks an already registered system