validate all nested arguments instead of using type=raw

[ktdreyer]

Ansible 2.6+ allows nested options in the argument specification we pass into the constructor with AnsibleModule(argument_spec=...). This would replace our use of raw types in argument_spec, and it would allow us to validate user input even earlier. It might even do these string -> None or string -> int conversions for us that we are doing within koji_tag.py's normalize_inheritance().

This feature is documented at https://docs.ansible.com/ansible/latest/dev_guide/developing_program_flow_modules.html#argument-spec