Properly compute Release and Version
    
    When Release is not specified, we should increase the current value by
    1. However, if that value is provided, we should get rid of what is
    found in the current spec.
    Same thing can be applied to the version field, except for the fact
    we don't increase that value (or at least, the logic of increasing it
    is unknown for now).
    
    Signed-off-by: Francesco Pantano <fpantano@redhat.com>