Depends on D20779. Ref T13403. Bad parameters may cause this call to fail without setting an error code; if it does, catch the issue and go down the normal connection error pathway.

• With "mysql.port" set to "quack", ran bin/storage probe.
• Before: wild mess of warnings as the code continued below and failed when trying to interact with the connection.
• After: clean connection failure with a useful error message.