vab support: merges and unmapping super devices

- check for merges before formatting data
- add advanced option for unmapping super devices

Change-Id: I38d4d3bbdfa071969016c3e000c86a4d03c71e45

data.cpp

@@ -786,7 +786,11 @@ void DataManager::SetDefaultValues()
 #else
 	mPersist.SetValue(TW_NO_SHA2, "1");
 #endif
+#ifdef AB_OTA_UPDATER
+	mPersist.SetValue(TW_UNMOUNT_SYSTEM, "0");
+#else
 	mPersist.SetValue(TW_UNMOUNT_SYSTEM, "1");
+#endif
 
 #ifdef TW_NO_SCREEN_TIMEOUT
 	mConst.SetValue("tw_screen_timeout_secs", "0");