Add `kube-reserved` and `system-reserved` flags for configuration
reserved resources for usage outside of kubernetes pods. Allocatable is
provided by the Kubelet according to the formula:
```
Allocatable = Capacity - KubeReserved - SystemReserved
```
Also provides a method for estimating a reasonable default for
`KubeReserved`, but the current implementation probably is low and needs
more tuning.
Change all references to the container ID in pkg/kubelet/... to the
strong type defined in pkg/kubelet/container: ContainerID
The motivation for this change is to make the format of the ID
unambiguous, specifically whether or not it includes the runtime
prefix (e.g. "docker://").
Add a new latency metric for the time from seeing the pod for the first time
to starting a pod worker for it.
Also, change PodStartLatency to include this initial processing latency.
