Stub out code for a host driven StagedRollbackTest.

The test doesn't test anything meaningful yet, but it builds and runs.

Bug: 124043688
Test: atest StagedRollbackTest
Change-Id: If9b5d57e28846b0ba28a580b74a486bbedb8f8d5
diff --git a/tests/RollbackTest/README.txt b/tests/RollbackTest/README.txt
index 110088b..c0b718a 100644
--- a/tests/RollbackTest/README.txt
+++ b/tests/RollbackTest/README.txt
@@ -5,6 +5,9 @@
 RollbackTest
   - device driven test for rollbacks not involving staged rollbacks.
 
+StagedRollbackTest
+  - device driven test for staged rollbacks.
+
 TestApp
   - source for dummy apks used in testing.
 
@@ -17,3 +20,4 @@
 You can manually run the tests as follows:
 
   atest RollbackTest
+  atest StagedRollbackTest