Add isctest.query.tls() function

Add isctest.query.tls() function

When explicitly set to True, the "verify" argument lets dnspython verify
certificates used for the connection. As most certificates in the system
test will inevitably be self-signed, the "verify" argument defaults to
False.

The "verify" argument is present in dnspython since the version 2.5.0.

(cherry picked from commit df8c419058e1e43265928b59f4ae54293f9a32de)