Interactor Style Command Rollback

This version updates command logic in two ways

• When a command fails it does not call its rollback method
• When an invoked command fails, the invoker does not roll
  it back (but it does roll back the commands prior to it
  that succeeded)

This follows from the idea that a command should have one responsibility so if it fails it does not need to be rolled back. This is how the interactor gem handles it: https://github.com/collectiveidea/interactor#rollback

We need this behavior for Adama to work as a drop-in replacement for Interactor