Automatic merge from submit-queue (batch tested with PRs 54761, 54748, 53991, 54485, 46951). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Enhanced the network policy describer.

**Which issue this PR fixes**: Fixes https://github.com/kubernetes/kubectl/issues/17

**Special notes for your reviewer**: I need help to set up the right clientset for the unt tests

@kubernetes/sig-network-pr-reviews 

ping @adohe 

As suggested in https://github.com/kubernetes/kubectl/issues/17 , the output is similar to:
```
Name:           access-backend
Namespace:      default
Created on:     2017-06-04 21:45:56 -0700 PDT
Labels:         <none>
Annotations:    <none>
Spec:
  Pod Selector:     foo in (bar1,bar2),foo2 notin (bar1,bar2),id=app1,id2=app3
  Allowing ingress traffic:
    To Port: 80/TCP
    To Port: 82/TCP
    From Pod Selector: id=app2,id2=app3
    From Namespace Selector: id=app2,id2=app3
    From Namespace Selector: foo in (bar1,bar2),id=app2,id2=app3
    ----------
    To Port: <any> (traffic allowed to all ports)
    From: <any> (traffic not restricted by source)
```