Share logic for calling postConnect method

This should be called on success, when we're creating primary
connection.

Signed-off-by: Michal Čihař <michal@cihar.com>
Do not call DBI->postConnect for control link

It used to just return, so there is no sense in calling it at all.

Signed-off-by: Michal Čihař <michal@cihar.com>