When unknown keyword arguments are passed to a Command, raise an
error instead of ignoring them.
Options used when IPA calls its commands internally are listed
in a new Command attribute called internal_options, and allowed.
Previous patches (0b01751c, c45174d6, c5689e7f) made IPA not use
unknown keyword arguments in its own commands and tests, but since
that some violations were reintroduced in permission_find and tests.
Fix those.
Tests included; both a frontend unittest and a XML-RPC test via the
ping plugin (which was untested previously).
https://fedorahosted.org/freeipa/ticket/2509
