Use doseq=True when re-encoding url query parameters

The query parameters are parsed out of a string using
urlparse.parse_qs, which produces a dictionary whose values
are lists of values.

The query parameters are then stuffed back into a string
using urlencode.urlencode, which uses percent-encoding to
encode lists as literal sequences of brackets and commas,
resulting in parse_qs and urlencode not being inverse
operations.

This change adds the doseq flag to urlencode, thus making
it encode each value from the list of values as a separate
key=value pair, thus making it a true inverse of parse_qs.

R=dnj@chromium.org

Change-Id: Ic4631cc672f9e42ba371306efdda71892d625119
Reviewed-on: https://chromium-review.googlesource.com/575398Reviewed-by: Daniel Jacques <dnj@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

recipes/recipe_modules/gitiles/resources/gerrit_client.py

@@ -34,7 +34,7 @@ def reparse_url(parsed_url, query_params):
       path=parsed_url.path,
       params=parsed_url.params,
       fragment=parsed_url.fragment,
-      query=urllib.urlencode(query_params))
+      query=urllib.urlencode(query_params, doseq=True))
 
 
 def gitiles_get(parsed_url, handler, attempts):