Fix a bug in print_list when using formatters

If using formatters it will raise a error that local variable
'data' referenced before assignment

story: 2008472
task: 41511
Change-Id: I6c66139b54a203bd8af01e8534e4d7ce7735e02d

Author: zhangjunhui

troveclient/utils.py

@@ -173,7 +173,7 @@ def print_list(objs, fields, formatters={}, order_by=None, obj_is_dict=False,
         row = []
         for field in fields:
             if formatters and field in formatters:
-                row.append(formatters[field](obj))
+                data = formatters[field](obj)
             elif obj_is_dict:
                 data = obj.get(field, '')
             else: