beaker-tests: several other fixes
    
    - use 'dnf copr enable NAMESPACE/COPR/USER', not just COPR/USER,
      this is better than patch dnf-plugins-core sources (available
      feature in new dnf-plugins-core)
    - move hello2 and beakerhello packages to @copr/ namespace
    - create a fork of passwd.git which I/we can update
    - repo file names have changed in new dnf-plugins-core
    - use 'dnf copr remove' to really remove the repofiles