backup.sh script does not work if master name does not contain "master"

[QSchulz]

In boards.yml file, a "name" needs to be assigned to each master node. This name does not need to contain "master" string in it to work. However, the backup.sh script actually expects the docker container to contain "master" string in it: https://github.com/kernelci/lava-docker/blob/master/backup.sh#L13

One could use yq to parse the boards.yaml file and return the name used for each master node. e.g.:

podman run --rm -i -v "${PWD}":/workdir:rw,Z mikefarah/yq '.masters[].name' < boards.yaml

Would that be something acceptable to run a container inside backup.sh to parse the yaml file?

Ideally we could use docker-compose to run commands for one of the master containers running but I still think we need the name of the container anyways.

Also, this wouldn't work with multiple master nodes but that's a different topic.