Handle duplicate headers in the uri module (#33792)

* Handle duplicate headers, and make it easier for users to use cookies, by providing a pre-built string

* Ensure proper cookie ordering, make key plural

* Add note about cookie sort order

* Add tests for duplicate headers and cookies_string

* Extend tests, normalize headers between py2 and py3

* Add some notes in test code

* Don't use AttributeError, use six.PY3. Use better names.

test/integration/targets/uri/tasks/main.yml

@@ -375,6 +375,17 @@
   failed_when: result is not failed
   when: has_httptester
 
+- uri:
+    url: https://{{ httpbin_host }}/response-headers?Set-Cookie=Foo%3Dbar&Set-Cookie=Baz%3Dqux
+  register: result
+
+- assert:
+    that:
+      - result['set_cookie'] == 'Foo=bar, Baz=qux'
+      # Python sorts cookies in order of most specific (ie. longest) path first
+      # items with the same path are reversed from response order
+      - result['cookies_string'] == 'Baz=qux; Foo=bar'
+
 - name: Write out netrc template
   template:
     src: netrc.j2