Improve archive upload/download integration

[heralden]

Build upon the work done in #20

I think it would be a good idea to move the code out of docker.py and into its own file, as it's not very docker related (perhaps archive.py).

We should also use envvars instead of the dict defined in the source file. We can then uncomment the function calls in commands.py and put in a statement to exit early out of the docker.upload_archives and docker.download_archives functions if the AWS envvars aren't defined.

In commands.py, I think it makes sense to place docker.upload_archives under build and docker.download_archives under start. We would then also have to modify the start process to unpack the archive and use it, instead of building from scratch (this is a slightly bigger task than the above points).

[22PoojaGaur]

Hi @uosl

created a PR for this.

We should include the last part (unpack and use archive) in this PR or a separate PR?

[heralden]

It's totally fine to include it in a separate PR. 👍