Handle service_del with bad service name
The command 'ipa service-del badservice' used to fail with an internal
server error, because check_required_principal() could not handle a
principal that is not a service principal. All del commands have less
strict error checking of primary keys so they can reference any stored
key, even illegal ones.
check_required_principal() skips required principal check if the
principal is not a service principal. A non-service principal can never
be a required principal.
Signed-off-by: Christian Heimes <firstname.lastname@example.org>
Reviewed-By: Alexander Bokovoy <email@example.com>