Objects: Make OPTIONAL_FIELDS a tuple

In some objects this is a list, in some it is a tuple.

Just use tuples for consistency.

Change-Id: I14871e2abd8680db72ab8e3d9ca873cb608e4039

cinder/objects/base.py

@@ -246,7 +246,7 @@ class CinderPersistentObject(object):
 
     This adds the fields that we use in common for all persistent objects.
     """
-    OPTIONAL_FIELDS = []
+    OPTIONAL_FIELDS = ()
 
     Not = db.Not
     Case = db.Case

cinder/objects/cgsnapshot.py

@@ -28,7 +28,7 @@ class CGSnapshot(base.CinderPersistentObject, base.CinderObject,
     # Version 1.1: Added from_group_snapshot
     VERSION = '1.1'
 
-    OPTIONAL_FIELDS = ['consistencygroup', 'snapshots']
+    OPTIONAL_FIELDS = ('consistencygroup', 'snapshots')
 
     # NOTE: When adding a field obj_make_compatible needs to be updated
     fields = {

cinder/objects/group.py

@@ -32,7 +32,7 @@ class Group(base.CinderPersistentObject, base.CinderObject,
     # Version 1.2: Added replication_status
     VERSION = '1.2'
 
-    OPTIONAL_FIELDS = ['volumes', 'volume_types', 'group_snapshots']
+    OPTIONAL_FIELDS = ('volumes', 'volume_types', 'group_snapshots')
 
     # NOTE: When adding a field obj_make_compatible needs to be updated
     fields = {

cinder/objects/group_snapshot.py

@@ -26,7 +26,7 @@ class GroupSnapshot(base.CinderPersistentObject, base.CinderObject,
                     base.CinderObjectDictCompat, base.ClusteredObject):
     VERSION = '1.0'
 
-    OPTIONAL_FIELDS = ['group', 'snapshots']
+    OPTIONAL_FIELDS = ('group', 'snapshots')
 
     # NOTE: When adding a field obj_make_compatible needs to be updated
     fields = {

cinder/objects/group_type.py

@@ -27,7 +27,7 @@ class GroupType(base.CinderPersistentObject, base.CinderObject,
     # Version 1.0: Initial version
     VERSION = '1.0'
 
-    OPTIONAL_FIELDS = ['group_specs', 'projects']
+    OPTIONAL_FIELDS = ('group_specs', 'projects')
 
     # NOTE: When adding a field obj_make_compatible needs to be updated
     fields = {

cinder/objects/qos_specs.py

@@ -33,7 +33,7 @@ class QualityOfServiceSpecs(base.CinderPersistentObject,
     #   1.0: Initial version
     VERSION = "1.0"
 
-    OPTIONAL_FIELDS = ['volume_types']
+    OPTIONAL_FIELDS = ('volume_types',)
 
     # NOTE: When adding a field obj_make_compatible needs to be updated
     fields = {

cinder/objects/volume_attachment.py

@@ -33,7 +33,7 @@ class VolumeAttachment(base.CinderPersistentObject, base.CinderObject,
     # Version 1.3: Added the connector attribute.
     VERSION = '1.3'
 
-    OPTIONAL_FIELDS = ['volume']
+    OPTIONAL_FIELDS = ('volume',)
     obj_extra_fields = ['project_id', 'volume_host']
 
     # NOTE: When adding a field obj_make_compatible needs to be updated