Additional certificates support for an apk.

Change-Id: I5b35d5728ba9d65f7ece956127270a9ca2ea0efe
diff --git a/core/package.mk b/core/package.mk
index 358caee..3af1afb 100644
--- a/core/package.mk
+++ b/core/package.mk
@@ -376,6 +376,9 @@
 PACKAGES.$(LOCAL_PACKAGE_NAME).PRIVATE_KEY := $(private_key)
 PACKAGES.$(LOCAL_PACKAGE_NAME).CERTIFICATE := $(certificate)
 
+$(LOCAL_BUILT_MODULE): PRIVATE_ADDITIONAL_CERTIFICATES := $(foreach c,\
+    $(LOCAL_ADDITIONAL_CERTIFICATES), $(c).x509.pem $(c).pk8)
+
 # Define the rule to build the actual package.
 $(LOCAL_BUILT_MODULE): $(AAPT) | $(ZIPALIGN)
 ifdef LOCAL_DEX_PREOPT