Upgrade strategy improvements

[shaoxt]

Is this a BUG REPORT or FEATURE REQUEST?:
improvements

What happened:

• One by one upgrade strategy is not fast enough to get 500-1000 nodes cluster done in short period time.
• To see whether there is any delay could be avoided in the termination or new node joining.
• To see whether any strategy could balance reliability and upgrade speed.

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• rolling-upgrade-controller version
• Kubernetes version :

$ kubectl version -o yaml

Other debugging information (if applicable):

• RollingUpgrade status:

$ kubectl describe rollingupgrade <rollingupgrade-name>

• controller logs:

$ kubectl logs <rolling-upgrade-controller pod>