clufter.spec: make setuptools and lxml python2-qualified for Py2
    
    Following, belatedly, the Fedora's progress towards specific Python
    branch qualified RPM packages for delivering reusable bits ("packages"
    in Python's sense) for the particular language run-time, move away
    from previously generic "python-" prefixes meant to be resolved as
    Python 2 packages onto "python2-" expressly indicating that also for
    lxml and setuptools:
    
    - python2-lxml introduced in Fedora 24 updates at latest:
      https://src.fedoraproject.org/rpms/python-lxml/c/f61642a334756d87c11d09be8bf1e2c0e74eacd7
    
    - python2-setuptools introduced in Fedora 24 at latest (though the
      virtual Provides was introduced even earlier):
      https://src.fedoraproject.org/rpms/python-setuptools/c/dcb79cee693f826f814b3b41ccc354009748e8a0
    
    Note: Fedora 24 was EOL'd on 2017-08-08:
          https://fedoraproject.org/wiki/End_of_life
    
    Also unify the Requires ordering between python2- and python3- packages.
    
    Signed-off-by: Jan Pokorný <jpokorny@redhat.com>