fix matrix report aggregation bug

We can't use ```endRun```, because endRun is not async. endRun isn't executed right after matrix build finishing, but it's executed according its queue. So, with using jclouds, often endRun is executed, when slave is shutdown already
That's not good at all -- you cannot store build-specifit info in the builder, because it can be used concurrently in several job runs.