build_image: Respect boot_images directory existence.

Kernel boot_images directory might be already created
by board specific setup code, respect its existence.

BUG=b:144912747
TEST=./build_image --board eve-manatee

Change-Id: I5d5d281c239e5b296b7a30f456c410e99f12e928
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/1940358
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Tomasz Jeznach <tjeznach@chromium.org>
Tested-by: Tomasz Jeznach <tjeznach@chromium.org>
1 file changed