7046557: Changes to the Java DB README files in JDK7

Summary: Update <jdkroot>/README.html with correct mention of Java DB, add JDK specific README files to <jdkroot>/db and <jdkroot>/demo/db.
Reviewed-by: ohair

make/common/Release.gmk

@@ -900,8 +900,10 @@ initial-image-jdk-db: $(DB_ZIP_LIST)
 	for d in $(DB_ZIP_LIST); do \
           ($(CD) $(JDK_IMAGE_DIR)/db && $(UNZIP) -o $$d); \
 	done
+	$(CP) $(ABS_DB_PATH)/README-JDK.html $(JDK_IMAGE_DIR)/db
 	$(RM) -rf $(DEMODIR)/db
 	$(MV) $(JDK_IMAGE_DIR)/db/demo $(DEMODIR)/db
+	$(CP) $(ABS_DB_PATH)/README-JDK-DEMOS.html $(DEMODIR)/db/
 	$(RM) $(JDK_IMAGE_DIR)/db/index.html $(JDK_IMAGE_DIR)/db/register.html
 endif