Add --disable_verity_computation flag to delta_generator

VABC doesn't support writing hash tree yet, provide an option to disable
for now

Test: treehugger
Bug: 168554689
Change-Id: I7bbb76b33b46b44101fc3ca6cee2c9ee85e2e82d
diff --git a/scripts/brillo_update_payload b/scripts/brillo_update_payload
index 32bb92c..1e729bd 100755
--- a/scripts/brillo_update_payload
+++ b/scripts/brillo_update_payload
@@ -193,6 +193,9 @@
   DEFINE_string disable_fec_computation "" \
     "Optional: Disables the on device fec data computation for incremental \
 update. This feature is enabled by default."
+  DEFINE_string disable_verity_computation "" \
+    "Optional: Disables the on device verity computation for incremental \
+update. This feature is enabled by default."
   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."
@@ -687,6 +690,10 @@
       GENERATOR_ARGS+=(
         --disable_fec_computation="${FLAGS_disable_fec_computation}" )
     fi
+    if [[ -n "${FLAGS_disable_verity_computation}" ]]; then
+      GENERATOR_ARGS+=(
+        --disable_verity_computation="${FLAGS_disable_verity_computation}" )
+    fi
   fi
 
   # minor version is set only for delta or partial payload.