Description of problem:
When I'm running through proxy which is stopped, yum fails (which is OK), but it fails with different exception than expected.


Version-Release number of selected component (if applicable):
yum-rhn-plugin-0.5.4-26.el5
yum-3.2.22-38.el5


How reproducible:
always


Steps to Reproduce:
1. Register yourself to RHN (RHN Satellite in my case)
2. Configure yum-rhn-plugin to run through proxy
   # grep -i proxy /etc/sysconfig/rhn/up2date | grep -v comment
   enableProxyAuth=1
   enableProxy=1
   proxyPassword=proxy_password
   proxyUser=proxy_user
   httpProxy=localhost:3128
3. Stop the proxy
   # service squid stop
4. Try to install some package from RHN channel
   # yum install -y test-package


Actual results:
# yum install -y test-regular-mon07nov2011_12_56_42_27745-0.1-1
Loaded plugins: rhnplugin
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in ?
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 309, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 157, in main
    base.getOptionsConfig(args)
  File "/usr/share/yum-cli/cli.py", line 187, in getOptionsConfig
    self.conf
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 665, in <lambda>
    conf = property(fget=lambda self: self._getConfig(),
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 254, in _getConfig
    self.plugins.run('init')
  File "/usr/lib/python2.4/site-packages/yum/plugins.py", line 179, in run
    func(conduitcls(self, self.base, conf, **kwargs))
  File "/usr/lib/yum-plugins/rhnplugin.py", line 148, in init_hook
    conduit.error(0, COMMUNICATION_ERROR + "\n" + CHANNELS_DISABLED + 
  File "/usr/lib/python2.4/site-packages/yum/Errors.py", line 32, in __str__
    return "%s" %(self.value,)
AttributeError: CommunicationError instance has no attribute 'value'


Expected results:
Error message should state there is a problem with connection.


Additional info:
From code inspection this seems to be caused by a mishmash of which variable yum and yum-rhn-plugin are using to store exception string:

=== yum uses self.value in its exceptions ===
# vim /usr/lib/python2.4/site-packages/yum/Errors.py
class YumBaseError(Exception):
    """
    Base Yum Error. All other Errors thrown by yum should inherit from
    this.
    """
    def __init__(self, value=None):
        Exception.__init__(self)
        self.value = value
    def __str__(self):
        return "%s" %(self.value,)

=== yum-rhn-plugin uses self.errmsg ===
# vim /usr/share/rhn/up2date_client/up2dateErrors.py
class Error(YumBaseError):
    """base class for errors"""
    def __init__(self, errmsg):
        self.errmsg = errmsg
        self.log = up2dateLog.initLog()

    def __repr__(self):
        self.log.log_me(self.errmsg)
        return self.errmsg