Run two microdroid test case as postsubmit

I have broken microdroid tests quite many times when I modify build
system. Adding some key test modules as presubmit will prevent the
similar breakage in the future.

This this CL, the tests are first added as postsubmit to satisfy the SLO
requirement. Then this will get promoted to presubmit.

Bug: N/A
Test: watch TH
Change-Id: I4a294af396f9a614b550df5e72b20afb8a138d6a

TEST_MAPPING

@@ -3,5 +3,14 @@
     {
       "path": "packages/modules/SdkExtensions"
     }
+  ],
+
+  "postsubmit": [
+    {
+      "name": "MicrodroidHostTestCases"
+    },
+    {
+      "name": "MicrodroidTestApp"
+    }
   ]
 }