f20 fix full path for container-prep

BUG=None
TEST=chromite.api.TestService/BuildTestServiceContainers

Change-Id: I6c16a48a5ba1e92cd913cc3eec4c8644626ccedd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/3144237
Reviewed-by: Sean McAllister <smcallis@google.com>
Reviewed-by: Jesse McGuire <jessemcguire@google.com>
Reviewed-by: Seewai Fu <seewaifu@google.com>
Reviewed-by: Congbin Guo <guocb@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Tested-by: Sean McAllister <smcallis@google.com>
1 file changed