docker image size of kube-batch is too big

[asifdxtreme]

Use Alpine image instead of ubuntu:18.04 for building kube-batch docker image, this will reduce the size of docker image considerably

Is this a BUG REPORT or FEATURE REQUEST?:
BUG REPORT

Uncomment only one, leave it on its own line:

/kind bug
/kind feature

What happened:
docker image size is too big
What you expected to happen:
docker image should be small <10MB
How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version):
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[hex108]

Maybe we could use scratch or other minimal image as base image?

cc @k82cn

[k82cn]

a minimal image, e.g. alpine, should be enough for this case.

[hex108]

/assign