[DeviceTests] Uninstall appx in try/catch

This should check if the app is installed first before it tries to uninstall, and run in a try/catch block to ensure it doesn't fail the build.

DeviceTests/build.cake

@@ -259,15 +259,16 @@ Task ("test-uwp-emu")
     .WithCriteria(IsRunningOnWindows())
     .Does (() =>
 {
-    // var uninstallPS = new Action (() => {
-    //    StartProcess ("powershell", $"Remove-AppxPackage -Package (Get-AppxPackage -Name {UWP_PACKAGE_ID}).PackageFullName");
-    // });
-
-    // try {
-    //    // Try to uninstall the app if it exists from before
-    //    uninstallPS();
-    // } catch { }
+    var uninstallPS = new Action (() => {
+        try {
+            StartProcess ("powershell",
+                $"$app = Get-AppxPackage -Name {UWP_PACKAGE_ID}; if ($app) { Remove-AppxPackage -Package $app.PackageFullName }");
+        } catch { }
+    });
 
+    // Try to uninstall the app if it exists from before
+    uninstallPS();
+    
     // Install the appx
     var appxBundlePath = GetFiles("./**/AppPackages/**/*.appxbundle").First ();
     Information("Installing appx: {0}", appxBundlePath);
@@ -289,7 +290,7 @@ Task ("test-uwp-emu")
     AddPlatformToTestResults(UWP_TEST_RESULTS_PATH, "UWP");
 
     // Uninstall the app (this will terminate it too)
-    // uninstallPS();
+    uninstallPS();
 });
 
 RunTarget(TARGET);