Create sandbox and container from yaml

[feiskyer]

Create sandbox and container from yaml, e.g.

sandbox.yaml

metadata:
  attempt: 1
  name: busybox-sandbox
  namespace: default
  uid: hdishd83djaidwnduwk28
linux:
  namespaces:
    options: {}

container.yaml

metadata:
  name: busybox4
image:
  image: busybox:latest
command:
- top

Fixes: #93

[xlgao-zju]

LGTM