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.
Ah, my mistake. No, this makes much more sense. In that case, either:
1. Rename the data member to be camel case, kill the comment and include seconds as part of the name or type.
2. Kill the struct and move the data member into OdbcConnection as described below.

Both seem like fine ways to go about it. Thanks!