Qbs: Make runMode of QbsRunConfiguration more consistent

Make sure to refresh the runMode if it is changed by Qbs. Make any
user change stick though.

Task-number: QTCREATORBUG-12947
Change-Id: Ie03fad764f1a4d927213ecbb226c0aecfcf791a5
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>