QmlProfiler: Avoid idle engine cancelling other engine's process

Task-number: QTCREATORBUG-9643

Change-Id: Ia0a2427a186fd9ad24e1cf620df48be13032a69b
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>