Test endpoint using the set SQL_LOGIN_TIMEOUT value

With this change when the entered endpoint is unreachable Tableau will
warn the user during connection setup instead of proceeding with an
incorrect endpoint and failing during query time. The timeout value set
by Tableau is used when testing the endpoint.
Future reference: You can assign a value straight to the data member when you declare it. `size_t loginTimeoutSeconds = 5;` would be sufficient.

I will make this change for you. Going to merge this in a minute.