Return stream log message on finger client failure

Return a message in the live log stream about failure to connect
to the executor providing the finger stream.

Change-Id: I6d111461096446550e541e26cf18486e6acbf189
diff --git a/zuul/web/__init__.py b/zuul/web/__init__.py
index 308c0c9..00ac9c6 100755
--- a/zuul/web/__init__.py
+++ b/zuul/web/__init__.py
@@ -100,9 +100,15 @@
         if not port_location:
             return (4011, "Error with Gearman")
 
-        await self._fingerClient(
-            ws, port_location['server'], port_location['port'], request['uuid']
-        )
+        try:
+            await self._fingerClient(
+                ws, port_location['server'], port_location['port'],
+                request['uuid']
+            )
+        except Exception as e:
+            self.log.exception("Finger client exception:")
+            msg = "Failure from finger client: %s" % e
+            ws.send_str(msg.decode('utf8'))
 
         return (1000, "No more data")