Mark standalone/vmservice/websocket_client_test as flaky on the vm

Filed issue 21387 to track this

R=iposva@google.com

Review URL: https://codereview.chromium.org//667383002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41241 260f80e4-7a28-3924-810f-c04153c831b5
Revert revision 41241

Issue 21387  seems to have already been fixed in 41240

Review URL: https://codereview.chromium.org//636283008

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41242 260f80e4-7a28-3924-810f-c04153c831b5