Use functools.wraps for check_resource decorator.

This helps runtime introspection tools like the `help()` builting or
IPython's `?` operator correctly find the underlying method instead of
the decorator definition.

docker/utils/decorators.py

@@ -1,7 +1,10 @@
+from functools import wraps
 from .. import errors
 
 
 def check_resource(f):
+
+    @wraps(f)
     def wrapped(self, resource_id=None, *args, **kwargs):
         if resource_id is None:
             if kwargs.get('container'):