Add prop for buildtype

Change-Id: I76efbb16f2e935f5736b19191a3a781006099929
diff --git a/config/common.mk b/config/common.mk
index 4e1f548..750d71a 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -187,5 +187,6 @@
     BUILD_DISPLAY_ID=$(BUILD_ID) \
     slim.ota.version=$(PRODUCT_VERSION_MAJOR).$(PRODUCT_VERSION_MINOR).$(PRODUCT_VERSION_MAINTENANCE) \
     ro.slim.version=$(SLIM_VERSION) \
-    ro.modversion=$(SLIM_MOD_VERSION)
+    ro.modversion=$(SLIM_MOD_VERSION) \
+    ro.slim.buildtype=$(SLIM_BUILD_TYPE)