Add __str__ and fix __len__ return type

Author: Max Rozentsveyg

third_party/2and3/boto/utils.pyi

@@ -167,8 +167,9 @@ class Password:
         hashfunc: Optional[Callable] = ...,
     ) -> None: ...
     def set(self, value: Union[bytes, _str]) -> None: ...
+    def __str__(self) -> _str: ...
     def __eq__(self, other: Any) -> bool: ...
-    def __len__(self) -> bool: ...
+    def __len__(self) -> int: ...
 
 def notify(
     subject: str,