build: Add support for defining products in /product

The build will now search for AndroidProducts.mk in /product

BUG: 22030305

Change-Id: I2d067d95d0c8dc1341a55167f9ac7f6926e04ce3
diff --git a/envsetup.sh b/envsetup.sh
index f838d62..245d5a2 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -1535,7 +1535,8 @@
 
 # Execute the contents of any vendorsetup.sh files we can find.
 for f in `test -d device && find -L device -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort` \
-         `test -d vendor && find -L vendor -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort`
+         `test -d vendor && find -L vendor -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort` \
+         `test -d product && find -L product -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null | sort`
 do
     echo "including $f"
     . $f