Fixed Bug:1400991 - Modified .off() logic for change events for dropdown.
ISSUE: The dropdowns had stopped working at Server-Manager due to previous fix where .off() handlers were introduced to stop triggering of multiple select2 change events
FIX: .off events are applied selectively and it just disables the change function and rest of the events remain unaffected

Change-Id: Ib2468ef9df52ac9fbc68c251be1bd92462b79344