Do not allow to modify access for public volume type

Now public volume type can be added/removed project access, but when
listing access, cinder returns 'Access list not available for public
volume types.' It's weird for users experience.

We should check if a type is public and do not allow public volume type
to modify project access.

APIImpact
When modifying access for public volume type, API will return 400 and message:
"Invalid volume type: Type access modification is not applicable to public
volume type."

Closes-Bug: #1467808

Change-Id: Id03eb3649ce02549c131c85697d8431c3f8c04dd

cinder/volume/volume_types.py

@@ -182,11 +182,21 @@ def get_volume_type_extra_specs(volume_type_id, key=False):
         return extra_specs
 
 
+def is_public_volume_type(context, volume_type_id):
+    """Return is_public boolean value of volume type"""
+    volume_type = db.volume_type_get(context, volume_type_id)
+    return volume_type['is_public']
+
+
 def add_volume_type_access(context, volume_type_id, project_id):
     """Add access to volume type for project_id."""
     if volume_type_id is None:
         msg = _("volume_type_id cannot be None")
         raise exception.InvalidVolumeType(reason=msg)
+    if is_public_volume_type(context, volume_type_id):
+        msg = _("Type access modification is not applicable to public volume "
+                "type.")
+        raise exception.InvalidVolumeType(reason=msg)
     return db.volume_type_access_add(context, volume_type_id, project_id)
 
 
@@ -195,6 +205,10 @@ def remove_volume_type_access(context, volume_type_id, project_id):
     if volume_type_id is None:
         msg = _("volume_type_id cannot be None")
         raise exception.InvalidVolumeType(reason=msg)
+    if is_public_volume_type(context, volume_type_id):
+        msg = _("Type access modification is not applicable to public volume "
+                "type.")
+        raise exception.InvalidVolumeType(reason=msg)
     return db.volume_type_access_remove(context, volume_type_id, project_id)