api-ref: add link to SLO docs from multipart-manifest=put param

Drive-by: run api-ref tox env under py3.

Change-Id: Iebce47eabcb3b198d4aa7c1b8cfaf8f53300f7f9

api-ref/source/conf.py

@@ -162,6 +162,11 @@ try:
 except OSError:
     warnings.warn('Cannot get last updated time from git repository. '
                   'Not setting "html_last_updated_fmt".')
+else:
+    if not isinstance(html_last_updated_fmt, str):
+        # for py3
+        html_last_updated_fmt = html_last_updated_fmt.decode('ascii')
+
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.

api-ref/source/parameters.yaml

@@ -1109,6 +1109,8 @@ multipart-manifest_put:
   description: |
     If you include the ``multipart-manifest=put`` query parameter, the object
     is a static large object manifest and the body contains the manifest.
+    See `Static large objects <https://docs.openstack.org/swift/latest
+    /api/large_objects.html#static-large-objects>`_ for more information.
   in: query
   required: false
   type: string

tox.ini

@@ -157,7 +157,7 @@ commands = sphinx-build -W -b html doc/source doc/build/html
 [testenv:api-ref]
 # This environment is called from CI scripts to test and publish
 # the API Ref to developer.openstack.org.
-basepython = python2.7
+basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf api-ref/build