vboot: move vboot_test.h to private namespace

BUG=b:124141368
TEST=make clean && make runtests
BRANCH=none

Change-Id: I48b390be1d7d9d4e17caddb883eed6eda3bd4ae6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2073212
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
1 file changed