Revert "Remove unused grains lookup"

This reverts commit 52be720d62cc601196f3405e090fb98511c86227.
Revert "Remove debugging pprint"

This reverts commit 4617a931be354f7e98a6999ed70d22cef70ed262.
Reintroduce the removed grains information.

Removed on 4617a931be354f7e98a6999ed70d22cef70ed262 and 52be720d62cc601196f3405e090fb98511c86227.
Adapt the runtests parser to support running the tests suite under a Docker container.
Include documentation about running the tests suite under a Docker container.
Merge pull request #8355 from s0undt3ch/features/docker-runtests

Run the tests suite under a docker container