tls_test: Add case to do a little checking of credentials_builder
tls_test: Add case to do a little checking of credentials_builder

Message-Id: <95c0e82fca984483f81b760b785d64a1b0ee7007@scylladb.com>

avikivity/seastar,syuu1228/seastar,dreamsxin/seastar,dreamsxin/seastar,avikivity/seastar,scylladb/seastar,cloudius-systems/seastar,kjniemi/seastar,avikivity/seastar,scylladb/seastar,scylladb/seastar,cloudius-systems/seastar,syuu1228/seastar,kjniemi/seastar,cloudius-systems/seastar,syuu1228/seastar,kjniemi/seastar,dreamsxin/seastar