This commit updates all files that weren't passing yamllint for them to
pass.
A new yamllint target has been added. One can run `tox -e yamllint` or
`yamllint -s .` locally to ensure yaml files are still passing.
This check will be enabled in the CI so it can get on every new
contributions, and prevent merging non-compliant code.
Signed-off-by: Yanis Guenane <yguenane@redhat.com>
