Add support for "skip_kernelblock_install"

CrOS could be used in devices that dont have custom firmware to
interpret the Kernelblock (Part2,4). In such devices skip trying
to make the kernelblock

BUG=none
TEST=./build_image --board=chronos test and verify we dont build the kernel block

Change-Id: I3e9a8dd765ea00db2ebf112553d96c08960e544f
Reviewed-on: https://gerrit.chromium.org/gerrit/40219
Commit-Queue: Anush Elangovan <anush@chromium.org>
Reviewed-by: Anush Elangovan <anush@chromium.org>
Tested-by: Anush Elangovan <anush@chromium.org>

build_library/base_image_util.sh

@@ -276,9 +276,9 @@ create_base_image() {
     USE_DEV_KEYS="--use_dev_keys"
   fi
 
+  if [[ ${skip_kernelblock_install} -ne 1 ]]; then
     # Place flags before positional args.
     ${SCRIPTS_DIR}/bin/cros_make_image_bootable "${BUILD_DIR}" \
-                                              ${image_name} \
-                                              ${USE_DEV_KEYS} \
-                                           --adjust_part="${FLAGS_adjust_part}"
+      ${image_name} ${USE_DEV_KEYS} --adjust_part="${FLAGS_adjust_part}"
+  fi
 }

build_library/dev_image_util.sh

@@ -109,9 +109,10 @@ EOF
   cleanup_mounts
   trap - EXIT
 
+  if [[ ${skip_kernelblock_install} -ne 1 ]]; then
     if should_build_image ${image_name}; then
       ${SCRIPTS_DIR}/bin/cros_make_image_bootable "${BUILD_DIR}" \
-                                                ${image_name} \
-                                                --force_developer_mode
+        ${image_name} --force_developer_mode
+    fi
   fi
 }

build_library/test_image_util.sh

@@ -81,10 +81,11 @@ mod_image_for_test () {
   cleanup_mounts
   trap - EXIT
 
+  if [[ ${skip_kernelblock_install} -ne 1 ]]; then
     # Now make it bootable with the flags from build_image.
     if should_build_image ${image_name}; then
       "${SCRIPTS_DIR}/bin/cros_make_image_bootable" "${BUILD_DIR}" \
-                                                  ${image_name} \
-                                                 --force_developer_mode
+         ${image_name} --force_developer_mode
+    fi
   fi
 }