Positive connection test in TestShadeSaslAuthenticationProvider runs with Kerberos instead of Shade authentication

The positive test (testPositiveAuthentication) in TestShadeSaslAuthenticationProvider doesn't create a new user in user1.doAs(), so it will use the already Kerberos authenticated user instead of re-authenticating with the token. 

As a consequence it doesn't reveal a problem introduced with HBASE-23881 which will cause clients to timeout if authenticated with a SASL mech which doesn't create a reply token in case of successful authentication.