scripts: Update the COS scripts

Adjust the path and make sure convert_image.sh & make_ova.sh works.

BUG=b/173643442
TEST=Manual Test
RELEASE_NOTE=None

Change-Id: I43af936c593529ba896d18ecbc0a910fe41d191b
Reviewed-on: https://cos-review.googlesource.com/c/third_party/platform/crosutils/+/10880
Tested-by: Roy Yang <royyang@google.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>