scripts: update cros_fuzz to $PATH/build_packages

cros_fuzz is still explicitly using
/mnt/host/source/src/scripts/build_packages. Migrate to build_packages
from chromite/bin. Update the old arguments to build_packages per the
warning messages.

BUG=none
TEST=cros_fuzz --board=amd64-generic reproduce --fuzzer
gstoraster_fuzzer --testcase $TESTCASE_PATH --package ghostscript-fuzz
--build-type msan

Change-Id: If45407eaafec7381fbacfa7f23b37af066521b36
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3680088
Commit-Queue: Paul Moy <pmoy@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Tested-by: Paul Moy <pmoy@chromium.org>
diff --git a/scripts/cros_fuzz.py b/scripts/cros_fuzz.py
index 9198234..0e25549 100644
--- a/scripts/cros_fuzz.py
+++ b/scripts/cros_fuzz.py
@@ -646,19 +646,17 @@
 
   logging.info('Building %s using %s.', package, build_type)
   extra_env = GetBuildExtraEnv(build_type)
-  build_packages_path = os.path.join(constants.SOURCE_ROOT, 'src', 'scripts',
-                                     'build_packages')
   command = [
-      build_packages_path,
+      'build_packages',
       '--board',
       board,
-      '--skip_chroot_upgrade',
+      '--skip-chroot-upgrade',
       package,
   ]
-  # For msan builds, always use "--nousepkg" since all package needs to be
+  # For msan builds, always use "--no-usepkg" since all package needs to be
   # instrumented with msan.
   if build_type == BuildType.MSAN:
-    command += ['--nousepkg']
+    command += ['--no-usepkg']
 
   # Print the output of the build command. Do this because it is familiar to
   # devs and we don't want to leave them not knowing about the build's progress