Add the onPayloadStarted callback API

The API is called back to the client when the payload starts in the VM.
The standard output from the payload is accessible via the
ParcelFileDescriptor argument as well.

Bug: 192904048
Test: run MicrodroidDemoApp and check that the payload output is shown.

Change-Id: Ie2afbb455496eec21617b94940ed4386a4865876
diff --git a/virtualizationservice/Android.bp b/virtualizationservice/Android.bp
index 0b8f2e5..40aa139 100644
--- a/virtualizationservice/Android.bp
+++ b/virtualizationservice/Android.bp
@@ -39,6 +39,7 @@
         "libuuid",
         "libvmconfig",
         "libzip",
+        "libvsock",
     ],
 }