Add a flag to manually override VABC

Test: generate an OTA with --disable_vabc
Change-Id: I4a42319584dc1388d097dba343fe3ace82479bec
diff --git a/scripts/brillo_update_payload b/scripts/brillo_update_payload
index 1e729bd..439a42a 100755
--- a/scripts/brillo_update_payload
+++ b/scripts/brillo_update_payload
@@ -200,6 +200,8 @@
     "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"
+  DEFINE_string disable_vabc "" \
+    "Optional: Disables Virtual AB Compression when installing the OTA"
 fi
 if [[ "${COMMAND}" == "hash" || "${COMMAND}" == "sign" ]]; then
   DEFINE_string unsigned_payload "" "Path to the input unsigned payload."
@@ -694,6 +696,10 @@
       GENERATOR_ARGS+=(
         --disable_verity_computation="${FLAGS_disable_verity_computation}" )
     fi
+    if [[ -n "${FLAGS_disable_vabc}" ]]; then
+      GENERATOR_ARGS+=(
+        --disable_vabc="${FLAGS_disable_vabc}" )
+    fi
   fi
 
   # minor version is set only for delta or partial payload.