volume_action doesn't always need names

for example, volume_list

salt/cloud/__init__.py

@@ -322,6 +322,7 @@ class CloudClient(object):
             return False
         if isinstance(names, str):
             names = names.split(',')
+
         ret = {}
         for name in names:
             volume_ = kwargs.copy()

salt/cloud/clouds/nova.py

@@ -831,3 +831,11 @@ def volume_attach(name, server_name, device='/dev/xvdb', **kwargs):
         device,
         timeout=300
     )
+
+
+def volume_list(**kwargs):
+    '''
+    Attach block volume
+    '''
+    conn = get_conn()
+    return conn.volume_list()

salt/modules/cloud.py

@@ -213,7 +213,7 @@ def volume_list(provider):
 
     '''
     client = _get_client()
-    info = client.volume_action(provider, action='list')
+    info = client.volume_action(provider, 'name', action='list')
     return info