Implement npv cover to show coverage of a CNP/CCNP

[yokaze]

Motivation

Currently, it takes some effort to list all the pods covered-by or excluded-by a CNP/CCNP.
Especially, it is beneficial if we can list the pods marked privileged and excluded by a CCNP.

How

Implement the following commands:

• npv cover ccnp <CCNP Name>
• npv cover cnp -n <Namespace> <CNP Name>
• --except flag to show all the endpoints outside of the coverage

NOTE: This command needs to query all the endpoints in a cluster, so performance is a concern.

Checklist

• Finish implementation of the issue
• Test all functions
• Have enough logs to trace activities
• Notify developers of necessary actions