rpm: depend on python2, not bare python
    
    Fedora requires packages to depend on "python2" RPM, not the unversioned
    "python" name. Fortunately even though RHEL-6 ships a "python" RPM, it
    has a virtual Provides for the "python2" name, so we don't need to
    conditionalize this.
    
    Reviewed-by: Andrea Bolognani <abologna@redhat.com>
    Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>