define full_boot flag in brillo_update_payload

Test: ota_from_target_files.py --full_boot
Change-Id: Id910b373f40d6c5eb814904383615f621e3f86d1

scripts/brillo_update_payload

diff --git a/scripts/brillo_update_payload b/scripts/brillo_update_payload
index 4137dfd..32bb92c 100755
--- a/scripts/brillo_update_payload
+++ b/scripts/brillo_update_payload
@@ -196,6 +196,7 @@
   DEFINE_string is_partial_update "" \
     "Optional: True if the payload is for partial update. i.e. it only updates \
 a subset of partitions on device."
+  DEFINE_string full_boot "" "Will include full boot image"
 fi
 if [[ "${COMMAND}" == "hash" || "${COMMAND}" == "sign" ]]; then
   DEFINE_string unsigned_payload "" "Path to the input unsigned payload."