Don't decode str in LogStreamingHandler

When we encounter an exception during log streaming we send an error
message through the websocket. However we decode the error message
which is already a str object which doesn't work. Thus the error
message will never arrive at the user. Fix that by just sending the
message.

Change-Id: I488cbfd2bb2f44f10921ab5a0cc16ae9ba4d2537
diff --git a/zuul/web/__init__.py b/zuul/web/__init__.py
index adbafb5..e962738 100755
--- a/zuul/web/__init__.py
+++ b/zuul/web/__init__.py
@@ -101,8 +101,7 @@
             )
         except Exception as e:
             self.log.exception("Finger client exception:")
-            msg = "Failure from finger client: %s" % e
-            await ws.send_str(msg.decode('utf8'))
+            await ws.send_str("Failure from finger client: %s" % e)
 
         return (1000, "No more data")