Add --leave_firmware_alone flag for BIOS testing purposes.

scripts/image_signing/tag_image.sh

Index: scripts/image_signing/tag_image.sh
diff --git a/scripts/image_signing/tag_image.sh b/scripts/image_signing/tag_image.sh
index 27a3764a9384c26d6f0bb64c61144a20ad2522a4..8ef7ff47418d137e3a52548d944c7f4c99b67cb3 100755
--- a/scripts/image_signing/tag_image.sh
+++ b/scripts/image_signing/tag_image.sh
@@ -18,6 +18,8 @@ DEFINE_string dev_mode "" \
   "(build-info) Tag as a developer mode build (1 to enable, 0 to disable)"
 DEFINE_string update_firmware "" \
   "(auto-update) Force updating firmware (1 to enable, 0 to disable)"
+DEFINE_string leave_firmware_alone "" \
+  "(auto-update) For BIOS development use ONLY (1 to enable, 0 to disable)"
 DEFINE_string forget_usernames "" \
   "(session-manager) Forget usernames (1 to enable, 0 to disable)"
 DEFINE_string leave_core "" \
@@ -142,6 +144,12 @@ process_all_tags() {
     "${FLAGS_update_firmware}"
 
   process_tag "${do_modification}" \
+    "(auto-update) leave_firmware_alone" \
+    "${rootfs}" \
+    /root/.leave_firmware_alone \
+    "${FLAGS_leave_firmware_alone}"
+
+  process_tag "${do_modification}" \
     "(session-manager) forget_usernames" \
     "${rootfs}" \
     /root/.forget_usernames \