Use Cinder API v3 as default

This patch sets Nova to use the Cinder v3 API as the default option.
This change uses the base '3.0' version, which is identical to v2.

Leveraging microversions that were introduced in v3 and switching to
a newer microversion will be added in a follow up patch.

Change-Id: Ibcc8eefcc5011ad5002d608a3c253f1e9b68416f

nova/conf/cinder.py

@@ -23,7 +23,7 @@ cinder_group = cfg.OptGroup(
 
 cinder_opts = [
     cfg.StrOpt('catalog_info',
-            default='volumev2:cinderv2:publicURL',
+            default='volumev3:cinderv3:publicURL',
             regex='(\w+):(\w+):(.*?)',
             help="""
 Info to match when looking for cinder in the service catalog.

nova/volume/cinder.py

@@ -88,6 +88,11 @@ def cinderclient(context):
     if version == '1':
         raise exception.UnsupportedCinderAPIVersion(version=version)
 
+    if version == '3':
+        # TODO(ildikov): Add microversion support for picking up the new
+        # attach/detach API that was added in 3.27.
+        version = '3.0'
+
     return cinder_client.Client(version,
                                 session=_SESSION,
                                 auth=auth,

releasenotes/notes/switch-to-cinder-v3-00bdf83e0937dbe5.yaml

@@ -0,0 +1,14 @@
+---
+upgrade:
+  - |
+    Nova is now configured to use the v3 version of the Cinder API. You need to
+    ensure that the v3 version of the Cinder API is available and listed in the
+    service catalog in order to use Nova with the default configuration option.
+
+    The base ``3.0`` version is identical to v2 and it was introduced in the
+    Newton release of OpenStack. In case you need Nova to continue using the v2
+    version you can point it towards that by setting the ``catalog_info``
+    option in the ``nova.conf`` file under the ``cinder`` section, like::
+
+        [cinder]
+        catalog_info = volumev2:cinderv2:publicURL