make metadata doc up to date

currently we have following output:

$ curl http://169.254.169.254/openstack
2012-08-10
2013-04-04
2013-10-17
2015-10-15
2016-06-30
2016-10-06
2017-02-22
latest

Change-Id: I6b4aed63d5c981abc9374baf929f05b26760e645

doc/source/user/metadata-service.rst

@@ -21,6 +21,10 @@ GET request to ``http://169.254.169.254/openstack``:
    2012-08-10
    2013-04-04
    2013-10-17
+   2015-10-15
+   2016-06-30
+   2016-10-06
+   2017-02-22
    latest
 
 To list supported versions for the EC2-compatible metadata API, make a GET
@@ -150,4 +154,4 @@ Instances can retrieve user data by making a GET request to
 
    $ curl http://169.254.169.254/2009-04-04/user-data
    #!/bin/bash
-   echo 'Extra user data here'
+   echo 'Extra user data here'

nova/api/metadata/base.py

@@ -63,6 +63,8 @@ VERSIONS = [
 # hidden from the listing, but can still be requested explicitly, which is
 # required for testing purposes. We know this isn't great, but its inherited
 # from EC2, which this needs to be compatible with.
+# NOTE(jichen): please update doc/source/user/metadata-service.rst on the
+# metadata output when new version is created in order to make doc up-to-date.
 FOLSOM = '2012-08-10'
 GRIZZLY = '2013-04-04'
 HAVANA = '2013-10-17'