Create composite disk image in VirtualizationService.

This is simpler than spawning mk_cdisk, and will also be useful for
making the payload image.

Bug: 190503456
Test: Ran microdroid, compared log output
Change-Id: Id67d6280696c4221b675eec99c65ea44e1c549ab
diff --git a/virtualizationservice/TEST_MAPPING b/virtualizationservice/TEST_MAPPING
new file mode 100644
index 0000000..6456a98
--- /dev/null
+++ b/virtualizationservice/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "presubmit": [
+    {
+      "name": "virtualizationservice_device_test"
+    }
+  ]
+}