[LAWS] Attempt to steal from all other workers instead of just one

The LAWS strategy, unlike the WS strategy, previously only attempted
to steal from one victim, instead of trying all other workers. This
probably caused SimpleActorTest to sporadically timeout, as all
workers went to sleep.

With this change, LAWS attempts, just like WS, to steal from all other
workers. In a next step, we may want to reduce the duplicated code
resulting from this.

Fixes #6.