Add an integration test for WebSocket

Summary:
**Motivation**

See if we can safely run a WebSocket test in Travis CI
Closes https://github.com/facebook/react-native/pull/11433

Differential Revision: D4342024

Pulled By: ericvicenti

fbshipit-source-id: 137fb0c39ed7ea3726e2778d5c0bdac4cef6ab89

Examples/UIExplorer/UIExplorerIntegrationTests/UIExplorerIntegrationTests.m

@@ -18,6 +18,14 @@
   [_runner runTest:_cmd module:@#name]; \
 }
 
+#define RCT_TEST_ONLY_WITH_PACKAGER(name) \
+- (void)test##name                        \
+{                                         \
+  if (getenv("CI_USE_PACKAGER")) {        \
+    [_runner runTest:_cmd module:@#name]; \
+  }                                       \
+}
+
 @interface UIExplorerIntegrationTests : XCTestCase
 
 @end
@@ -63,6 +71,7 @@ RCT_TEST(AppEventsTest)
 //RCT_TEST(LayoutEventsTest) // Disabled due to flakiness: #8686784
 RCT_TEST(SimpleSnapshotTest)
 RCT_TEST(PromiseTest)
+RCT_TEST_ONLY_WITH_PACKAGER(WebSocketTest)
 
 
 @end