Automatic merge from submit-queue

Increase default memory of vagrant slave nodes to 2048

With current default number (1024) i am not able to spawn all required for
e2e tests kube-system pods. I had problems with heapster replicas, and
it was obvious from kube-scheduler logs that it is in Pending exaclty because of
insufficient memory.

To reproduce:
1. KUBERNETES_PROVIDER=vagrant ./cluster/kube-up.sh
2. Run any e2e test