yum fails with "optparse.OptionConflictError: option --downloadonly: conflicting option string(s): --downloadonly"

Issue

• On attempting to upgrade packages, below errors are seen:

# yum clean all
Loaded plugins: downloadonly, product-id, refresh-packagekit, rhnplugin,
              : security, subscription-manager
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 300, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 115, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 229, in getOptionsConfig
    self.conf
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 911, in <lambda>
    conf = property(fget=lambda self: self._getConfig(),
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 335, in _getConfig
    startupconf.pluginconfpath,disabled_plugins,enabled_plugins)
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 564, in doPluginSetup
    plugin_types, confpath, disabled_plugins, enabled_plugins)
  File "/usr/lib/python2.6/site-packages/yum/plugins.py", line 167, in __init__
    self.run('config')
  File "/usr/lib/python2.6/site-packages/yum/plugins.py", line 184, in run
    func(conduitcls(self, self.base, conf, **kwargs))
  File "/usr/lib/yum-plugins/downloadonly.py", line 30, in config_hook
    default=False, help="don't update, just download")
  File "/usr/lib64/python2.6/optparse.py", line 1020, in add_option
    self._check_conflict(option)
  File "/usr/lib64/python2.6/optparse.py", line 995, in _check_conflict
    option)
optparse.OptionConflictError: option --downloadonly: conflicting option string(s): --downloadonly