cassandra results NO_METADATA flag bugs

[rukai]

I know that at least the datastax cpp driver will generate messages with this flag.

Currently there is a panic preventing us from enabling a prepared statement test case in prepared_statements_simple.rs due to a failure in cassandra_int_tests::cluster_single_rack_v3::case_1_datastax due to a null value in a no_metadata message.

We also completely fail to reencode no_metadata messages, everything turns into a Blob.
Further inspection and integration test have proved this wrong.