base_image_util: Tolerate multiple ARM kernels

Shell '-e' test can only be used on a single file name,
so if the glob matches multiple kernels, no kernels will be copied!

BUG=b/283954538
TEST=`build_image --board=gmec-arm64-hw` (to be committed)
RELEASE_NOTE=None

Change-Id: Ie200c5b051849533c98fc4a8e16a61b6ca9b612b
Reviewed-on: https://cos-review.googlesource.com/c/third_party/platform/crosutils/+/49831
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Meena Shanmugam <meenashanmugam@google.com>