Optimize Tutorial Build with Docker Images

[brianjo]

Tutorials currently runs the entire build from scratch multiple times for every PR merge.
Persisting a docker image after the tutorial build will allow us to do incremental builds on tutorials.
@seemethere and I met to discuss updating the build with this in mind and we think it's possible to persist the output of the build and do these incrementally.
We'll try to get this going over the next couple of weeks.

[malfet]

I wonder if we can re-use sccache for tutorial builds?

[brianjo]

Hey all, @v-jizhang is going to take a look at this. He's most recently worked on the Buck Circle CI builds. Thanks!

[v-jizhang]

@brianjo I'll take a look, thank you!

[v-jizhang]

I think we can utilize one of the CircleCI’s caching mechanisms DLC, Docker Layer Caching. What we need to do is to change the current steps into docker building steps(in file Dockerfile) based on the existing docker image (tag 291). By turning on DLC in config.yml, CircleCI will cache the layers(steps) automatically for us.