This should make 'no space left on device' problems easier to handle
Use /tmp/releases as local_release_dir CI created machine, while keeping
the same folder on the runner (needed for gitlab-ci runner pods)
We should not rollback our test setup during upgrade test.
The only reason to do that would be for incompatible changes in the test
inventory, and we already checkout master for those (${CI_JOB_NAME}.yml)
Also do some cleanup by removing unnecessary intermediary variables
