Add aws-cli to our tools image build to be pulled in to agent images

[stmcginnis]

The AWS CLI is used in the sonobuoy agent and will soon be used in the workload test agent. The source code for the AWS CLI is open source, located here:

https://github.com/aws/aws-cli

We should add this to the set of tools that are built in tools/Dockerfile so any agents that need this CLI can just copy it over. This also makes sure we are building from source rather than pulling down a binary directly.

[stmcginnis]

I spent a little time doing some quick investigation for this. This CLI may be a bit of a challenge, at least compared to the other tools we pull in through the dockerized build.

The main challenge is that the AWS cli is written in Python, which brings some additional challenges that we don't have with the other Go tools we pull in. The installation process that project uses assumes the user is going to download the finished package and run the install script to get everything in place.

Installing a python script as a single executable requires placing all of the Python source scripts into the correct location, then using something like setuptools to create a psuedo-binary that wraps the initialization to call the main function in those scripts. Due to this, we can't just build and copy out the aws binary like we do for the other tools.