The test now checks that both users with passwords and users without
passwords work through MaxScale when skip_authentication is enabled. In
addition to this, the test also makes sure that the wrong password and a
missing password are properly detected.
The result of the authentication should be ignored but the scramble that
is calculated as a side-effect still needs to be stored. This can be done
by altering the SQL used to get the matching row to only match on the
username, not the network address.
Also expanded the test case to cover the use of bad credentials.
