This also moves the methods load_mmd and load_mmd_file to
module_build_service.utils.general.
This also removes some MSE unit tests with a mix of positive and
negative streams since this is not supported in libmodulemd v2. The
user will be presented with a syntax error if they try to submit
such a modulemd file.
This commit introduces new to_text_type helper method and calls it
for return value of all mmd.dumps() calls. That way, we always
end up with proper unicode string represntation on both python
major versions.
This commit also adds unicode character to description of all
the yaml files we use in the tests so we can be sure MBS can
handle unicode characters properly.
This might be temporary fix, depending on the result of discussion
at https://github.com/fedora-modularity/libmodulemd/issues/184.
