Bug 1273201 - Disable unstable websockets test, a=testonly

MozReview-Commit-ID: G91irAXCba1

testing/web-platform/meta/websockets/interfaces/WebSocket/events/015.html.ini

@@ -1,11 +1,7 @@
 [015.html]
   type: testharness
-  expected:
-    if not debug and e10s and (os == "linux") and (version == "Ubuntu 12.04") and (processor == "x86_64") and (bits == 64): TIMEOUT
-  [WebSockets: instanceof on events]
-    expected:
-      if not debug and e10s and (os == "linux") and (version == "Ubuntu 12.04") and (processor == "x86_64") and (bits == 64): TIMEOUT
-
+  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1273201
 
 [015.html?wss]
+  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1273201
   type: testharness