Changed priorities of tasks scheduled by TimeoutWithErrorTask

The problem is described in SI-1658. You can find there traces attached, which demonstrate behavior before and after change of priorities in TimeoutWithErrorTask. Basic idea is to make execution of task which is being wrapped by TimeoutWithErrorTask right after timeout as been scheduled for it. One way of achieving it is to put it on top of the SerialExecutor's priority queue. I considered other options but couldn't find any nice solution without serious refactoring.