build_library: create_prod_sysexts: Move artifacts to BUILD_DIR

Putting things in a sysexts subdir results in the same layout on
bincache and does not follow the expected url schema for fetching the
sysext.

Signed-off-by: Jeremi Piotrowski <jpiotrowski@microsoft.com>

build_library/prod_image_util.sh

@@ -251,8 +251,6 @@ create_prod_tar() {
 create_prod_sysexts() {
   local image_name="$1"
   local image_sysext_base="${image_name%.bin}_sysext.squashfs"
-  sudo rm -rf "${BUILD_DIR}/sysexts/*"
-  mkdir -p "${BUILD_DIR}/sysexts"
   local to_upload=()
   for sysext in "${EXTRA_SYSEXTS[@]}"; do
     local name="flatcar-${sysext%:*}"
@@ -261,24 +259,27 @@ create_prod_sysexts() {
     if [[ ! -x "${mangle_script}" ]]; then
       mangle_script=
     fi
+    sudo rm -f "${BUILD_DIR}/${name}.raw" \
+	"${BUILD_DIR}/flatcar-test-update-${name}.gz" \
+	"${BUILD_DIR}/${name}_*"
     sudo "${SCRIPT_ROOT}/build_sysext" --board="${BOARD}" \
         --squashfs_base="${BUILD_DIR}/${image_sysext_base}" \
-	--image_builddir="${BUILD_DIR}/sysexts" \
+	--image_builddir="${BUILD_DIR}" \
 	${mangle_script:+--manglefs_script=${mangle_script}} \
 	"${name}" "${pkg}"
     delta_generator \
       -private_key "/usr/share/update_engine/update-payload-key.key.pem" \
       -new_image "${BUILD_DIR}/sysexts/${name}.raw" \
       -out_file "${BUILD_DIR}/sysexts/flatcar_test_update-${name}.gz"
     to_upload+=(
-        "${BUILD_DIR}/sysexts/${name}.raw"
-        "${BUILD_DIR}/sysexts/${name}_contents.txt"
-        "${BUILD_DIR}/sysexts/${name}_contents_wtd.txt"
-        "${BUILD_DIR}/sysexts/${name}_disk_usage.txt"
-        "${BUILD_DIR}/sysexts/${name}_packages.txt"
-        "${BUILD_DIR}/sysexts/flatcar_test_update-${name}.gz"
+        "${BUILD_DIR}/${name}.raw"
+        "${BUILD_DIR}/${name}_contents.txt"
+        "${BUILD_DIR}/${name}_contents_wtd.txt"
+        "${BUILD_DIR}/${name}_disk_usage.txt"
+        "${BUILD_DIR}/${name}_packages.txt"
+        "${BUILD_DIR}/flatcar_test_update-${name}.gz"
     )
   done
-  upload_image -d ${BUILD_DIR}/sysexts/sysext.DIGESTS "${to_upload[@]}"
+  upload_image -d ${BUILD_DIR}/sysexts.DIGESTS "${to_upload[@]}"
 }