Implement resource accounting for pods with the Mesos scheduler

This patch

- set limits (0.25 cpu, 64 MB) on containers which are not limited in pod spec
  (these are also passed to the kubelet such that it uses them for the docker
  run limits)
- sums up the container resource limits for cpu and memory inside a pod,
- compares the sums to the offered resources
- puts the sums into the Mesos TaskInfo such that Mesos does the accounting
  for the pod.
- parses the static pod spec and adds up the resources
- sets the executor resources to 0.25 cpu, 64 MB plus the static pod resources
- sets the cgroups in the kubelet for system containers, resource containers
  and docker to the one of the executor that Mesos assigned
- adds scheduler parameters --default-container-cpu-limit and
  --default-container-mem-limit.

The containers themselves are resource limited the Docker resource limit which
the kubelet applies when launching them.

Fixes mesosphere/kubernetes-mesos#68 and mesosphere/kubernetes-mesos#304

contrib/mesos/pkg/executor/config/config.go

@@ -26,4 +26,5 @@ const (
 	DefaultInfoSource     = "kubernetes"
 	DefaultInfoName       = "Kubelet-Executor"
 	DefaultSuicideTimeout = 20 * time.Minute
+	DefaultCgroupPrefix   = "mesos"
 )