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.
Great catch! I forgot to revise the signature of this function and a few others to use the proper handle types. Throwing out a pull request to fix this in a few minutes.