Use mysql.ParseDSN func instead of url.Parse

The MySQL DB driver has it's own DSN parsing function. Previously we
were using the url.Parse function, but this causes problems because a
valid MySQL DSN can be an invalid http URL, namely when using some
special characters in the password.

This change uses the MySQL DB driver's builtin ParseDSN function and
applies a timeout parameter natively via that.

Another benefit of this change is that we fail earlier if given an
invalid MySQL DSN.

closes #870
closes #1842