test: Fix mypy types (shaka-project#169)

On some versions, mypy thinks the file handle from the web server is BinaryIO, in others, BufferedIOBase.  We don't care which it is, as both have the methods we care about.

I tried the IOBase class from "io", but I get failures on certain devices.  This is the best solution I've found so far.

streamer/proxy_node.py

@@ -21,6 +21,7 @@
 import urllib.parse
 
 from http.server import ThreadingHTTPServer, BaseHTTPRequestHandler
+from io import BufferedIOBase
 from typing import Any, BinaryIO, Optional, Union
 
 from streamer.node_base import ProcessStatus, ThreadedNodeBase
@@ -198,7 +199,7 @@ def do_DELETE(self) -> None:
 
   @abc.abstractmethod
   def handle_non_chunked(self, path: str, length: int,
-                         file: BinaryIO) -> None:
+                         file: Union[BinaryIO, BufferedIOBase]) -> None:
     """Write the non-chunked data stream from |file| to the destination."""
     pass
 
@@ -236,7 +237,7 @@ def __init__(self, bucket: Any, base_path: str,
     super().__init__(rate_limiter, *args, **kwargs)
 
   def handle_non_chunked(self, path: str, length: int,
-                         file: BinaryIO) -> None:
+                         file: Union[BinaryIO, BufferedIOBase]) -> None:
     # No leading slashes, or we get a blank folder name.
     full_path = (self._base_path + path).strip('/')
     blob = self._bucket.blob(full_path)
@@ -297,7 +298,7 @@ def __init__(self, client: Any, bucket_name: str, base_path: str,
     super().__init__(rate_limiter, *args, **kwargs)
 
   def handle_non_chunked(self, path: str, length: int,
-                         file: BinaryIO) -> None:
+                         file: Union[BinaryIO, BufferedIOBase]) -> None:
     # No leading slashes, or we get a blank folder name.
     full_path = (self._base_path + path).strip('/')
     # length is unused here.