Add microversion to allow setting flavor description

This adds the new microversion to allow providing
a description when creating a flavor, returning a
flavor description when showing flavor details, and
updating the description on an existing flavor.

Implements blueprint flavor-description

Change-Id: Ib16b0de82f9f9492f5cacf646dc3165a0849d75e

nova/api/openstack/api_version_request.py

@@ -129,6 +129,7 @@ REST_API_VERSION_HISTORY = """REST API Version History:
              id field, and takes a uuid in requests. PUT and GET requests
              and responses are also changed.
     * 2.54 - Enable reset key pair while rebuilding instance.
+    * 2.55 - Added flavor.description to GET/POST/PUT flavors APIs.
 """
 
 # The minimum and maximum versions of the API supported
@@ -137,7 +138,7 @@ REST_API_VERSION_HISTORY = """REST API Version History:
 # Note(cyeoh): This only applies for the v2.1 API once microversions
 # support is fully merged. It does not affect the V2 API.
 _MIN_API_VERSION = "2.1"
-_MAX_API_VERSION = "2.54"
+_MAX_API_VERSION = "2.55"
 DEFAULT_API_VERSION = _MIN_API_VERSION
 
 # Almost all proxy APIs which are related to network, images and baremetal