Revert "Not running UITests until MUXTestInfra is fixed for preview2."

This reverts commit a77adc9.

Author: azchohfi

build/build.cake

@@ -360,7 +360,7 @@ Task("MSTestUITest")
 Task("Default")
     .IsDependentOn("Build")
     //.IsDependentOn("Test")
-    //.IsDependentOn("UITest")
+    .IsDependentOn("UITest")
     .IsDependentOn("Package");
 
 Task("UpdateHeaders")