Description of problem:
koji cli don't catch the error, when for the xml server the dns entry is mising.

Version-Release number of selected component:
koji-1.20.1-1.el7

Additional info:
reporter:       libreport-2.1.11.1
cmdline:        /usr/bin/python2 /usr/bin/koji -d --profile=mdc list-targets
executable:     /usr/bin/koji
kernel:         3.10.0-1062.18.1.el7.x86_64
pkg_fingerprint: 6A2F AEA2 352C 64E5
pkg_vendor:     Fedora Project
reproducible:   Not sure how to reproduce the problem
runlevel:       N 5
type:           Python
uid:            1000

Truncated backtrace:
adapters.py:415:send:ConnectionError: ('Connection aborted.', gaierror(-2, 'Name or service not known'))

Traceback (most recent call last):
  File "/usr/bin/koji", line 333, in <module>
    rv = locals()[command].__call__(options, session, args)
  File "/usr/lib/python2.7/site-packages/koji_cli/commands.py", line 3841, in anon_handle_list_targets
    activate_session(session, goptions)
  File "/usr/lib/python2.7/site-packages/koji_cli/lib.py", line 581, in activate_session
    ensure_connection(session)
  File "/usr/lib/python2.7/site-packages/koji_cli/lib.py", line 110, in ensure_connection
    ret = session.getAPIVersion()
  File "/usr/lib/python2.7/site-packages/koji/__init__.py", line 2187, in __call__
    return self.__func(self.__name, args, opts)
  File "/usr/lib/python2.7/site-packages/koji/__init__.py", line 2683, in _callMethod
    return self._sendCall(handler, headers, request)
  File "/usr/lib/python2.7/site-packages/koji/__init__.py", line 2601, in _sendCall
    return self._sendOneCall(handler, headers, request)
  File "/usr/lib/python2.7/site-packages/koji/__init__.py", line 2644, in _sendOneCall
    r = self.rsession.post(handler, **callopts)
  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 529, in post
    return self.request('POST', url, data=data, json=json, **kwargs)
  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 486, in request
    resp = self.send(prep, **send_kwargs)
  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 598, in send
    r = adapter.send(request, **kwargs)
  File "/usr/lib/python2.7/site-packages/requests/adapters.py", line 415, in send
    raise ConnectionError(err, request=request)
ConnectionError: ('Connection aborted.', gaierror(-2, 'Name or service not known'))

Local variables in innermost frame:
chunked: False
stream: True
err: ProtocolError('Connection aborted.', gaierror(-2, 'Name or service not known'))
url: '/'
verify: True
self: <requests.adapters.HTTPAdapter object at 0x7f12410bc310>
request: <PreparedRequest [POST]>
cert: None
timeout: <urllib3.util.timeout.Timeout object at 0x7f12410bc790>
proxies: {}
conn: <urllib3.connectionpool.HTTPSConnectionPool object at 0x7f12410bc7d0>