urllib.urlencode() does not exist for python3

This is similar to bug 1414055, but now for urlencode:

Traceback (most recent call last):
  File "apport/crashdb_impl/launchpad.py", line 1950, in test_marking_python_task_mangle
    t = b.bug_tasks[0]
  File "/usr/lib/python3/dist-packages/lazr/restfulclient/resource.py", line 853, in __getitem__
    found_slice = self._get_slice(slice(key, key + 1))
  File "/usr/lib/python3/dist-packages/lazr/restfulclient/resource.py", line 903, in _get_slice
    self._wadl_resource.url, 'ws.start', start)
  File "/usr/lib/python3/dist-packages/lazr/restfulclient/resource.py", line 976, in _with_url_query_variable_set
    uri.query = urllib.urlencode(params, True)
AttributeError: 'module' object has no attribute 'urlencode'

I suggest something like

if sys.version_info.major == 2:
    from urllib import urlencode
else:
    from urllib.parse import urlencode

and use urlencode() without namespace.