adjust channel_test to be less specific (#5721)

* adjust channel_test to be less specific
fixes https://github.com/flutter/flutter/issues/5716

packages/flutter_tools/test/channel_test.dart

@@ -19,10 +19,10 @@ void main() {
       expect(await runner.run(<String>['channel']), 0);
       BufferLogger logger = context[Logger];
       expect(logger.errorText, hasLength(0));
-      expect(logger.statusText, contains('channels'));
-      expect(logger.statusText, contains('master'));
-      // fails on bots
-      //expect(logger.statusText, contains('* ')); // current channel mark
+      // The bots may return an empty list of channels (network hiccup?)
+      // and when run locally the list of branches might be different
+      // so we check for the header text rather than any specific channel name.
+      expect(logger.statusText, contains('Flutter channels:'));
     });
   });
 }