Allow files generated by droidstubs to be copied in the SDK

We need to get files generated by a droidstubs target into the SDK. So
we first copy them into the out/target/common/obj/PACKAGING folder where
they can be picked up by the SDK build.

Bug: 142480924
Test: m sdk
Change-Id: I7a0b22907603e1d17ac05901ee7f8bb9cff89f7f
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 24cca5a..007235e 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -73,6 +73,7 @@
 LOCAL_DROIDDOC_DOC_ZIP :=
 LOCAL_DROIDDOC_JDIFF_DOC_ZIP :=
 LOCAL_DROIDDOC_HTML_DIR:=
+LOCAL_DROIDDOC_METADATA_ZIP:=
 LOCAL_DROIDDOC_OPTIONS:=
 LOCAL_DROIDDOC_SOURCE_PATH:=
 LOCAL_DROIDDOC_STUB_OUT_DIR:=