Add system propery ro.build.flavor.

ro.build.flavor is set to "$(TARGET_PRODUCT)-$(TARGET_BUILD_VARIANT)" in
system.img build.prop at build time,
and it won't be overridden by oem partition's build.prop.

Bug: 18605832
Change-Id: Ic917623dd43b74d9c601119db0b457483e8c4472
diff --git a/tools/buildinfo.sh b/tools/buildinfo.sh
index ed6bd87..a80b2db 100755
--- a/tools/buildinfo.sh
+++ b/tools/buildinfo.sh
@@ -16,6 +16,7 @@
 echo "ro.build.user=$USER"
 echo "ro.build.host=`hostname`"
 echo "ro.build.tags=$BUILD_VERSION_TAGS"
+echo "ro.build.flavor=$TARGET_BUILD_FLAVOR"
 echo "ro.product.model=$PRODUCT_MODEL"
 echo "ro.product.brand=$PRODUCT_BRAND"
 echo "ro.product.name=$PRODUCT_NAME"