Resource retrieving: add changes-before filter

This adds the changes-before filter to the servers,
os-instance-actions and os-migrations APIs for
filtering resources which were last updated before
or equal to the given time. The changes-before filter,
like the changes-since filter, will return deleted
server resources.

Part of bp support-to-query-nova-resources-filter-by-changes-before
Change-Id: If91c179e3823c8b0da744a9363906b0f7b05c326

doc/api_samples/versions/v21-version-get-resp.json

@@ -19,7 +19,7 @@
             }
         ],
         "status": "CURRENT",
-        "version": "2.65",
+        "version": "2.66",
         "min_version": "2.1",
         "updated": "2013-07-23T11:33:21Z"
     }

doc/api_samples/versions/versions-get-resp.json

@@ -22,7 +22,7 @@
                 }
             ],
             "status": "CURRENT",
-            "version": "2.65",
+            "version": "2.66",
             "min_version": "2.1",
             "updated": "2013-07-23T11:33:21Z"
         }