Add prebuilt image for python

[ybbbby]

Python image is built by Bazel from grpc/grpc, and can be further optimized.
After built, bone structure/binary is extracted to a new image to shrink the final image's size.
The build procedure mimic the init-containers' clone, build and run steps.
I have verified the prebuilt image on benchmark-prod reaching the same stage as regular multi-stage images.
The image size:

30b5098c98b6   30 seconds ago   /bin/sh -c #(nop) COPY file:1288b1d07ba39958…   52B       
2cc577ed0a38   22 hours ago     /bin/sh -c #(nop) COPY file:2119411c1149daf8…   4.99MB  

So approximately 8.43MB would be pushed to gcr.io.
Using prebuilt image, we can complete the performance test within 50s while we need 7m32s to finish using multi-stage images. Thus, we can save approximately 6m40s.

[wanlin31]

I think for this great work you have done, it will be nice to let reviewers know that:
(usually what I did, hopefully helpful :) )

(1) You have verified with benchmark-prod (deployed controller) or benchmark-dev1 (deployed controller or local controller run against cluster) using this image, and reach to the same stage as regular images. (I usually have this statement in the comment for the previous images, it is up to you how you want to verify it, but at least people know you have verified it)
(2) What is the size for the binary we need to push each time to the repositories.
I have done the analysis of this one, we will push ~8.43MB each time to gcr.io, looks great.

64227fbc6206   10 minutes ago   /bin/sh -c #(nop) COPY file:838ec40eee1c3cf3…   52B       
ed81bd397642   10 minutes ago   /bin/sh -c #(nop) COPY file:016ebc82536415ae…   8.43MB 

(3) How much is the time we saved for using pre-built image.

I have not went through cxx for these step in the comments is because it is part of the investigation and have been verified and reported several times, and for go, I have not yet mark the pr as ready, I will probably do the same thing as I described.

[wanlin31]

This apply to all the images, I leave it here so I won't flood all your PRs. :)

[ybbbby]

I think for this great work you have done, it will be nice to let reviewers know that:
(usually what I did, hopefully helpful :) )

(1) You have verified with benchmark-prod (deployed controller) or benchmark-dev1 (deployed controller or local controller run against cluster) using this image, and reach to the same stage as regular images. (I usually have this statement in the comment for the previous images, it is up to you how you want to verify it, but at least people know you have verified it)
(2) What is the size for the binary we need to push each time to the repositories.
I have done the analysis of this one, we will push ~8.43MB each time to gcr.io, looks great.

64227fbc6206   10 minutes ago   /bin/sh -c #(nop) COPY file:838ec40eee1c3cf3…   52B       
ed81bd397642   10 minutes ago   /bin/sh -c #(nop) COPY file:016ebc82536415ae…   8.43MB 

(3) How much is the time we saved for using pre-built image.

I have not went through cxx for these step in the comments is because it is part of the investigation and have been verified and reported several times, and for go, I have not yet mark the pr as ready, I will probably do the same thing as I described.

Thanks for pointing out!

[wanlin31]

I think Paulo already mentioned things I want to talk about. LGTM.