Add disconnect to post build groovy script

Task-number: QTQAINFRA-840

Change-Id: Ia1e9c53114c153656a85cc72f8d4cd9ca4892a23
Reviewed-by: Heikki Halmet <heikki.halmet@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>