Create a pipe between otapreopt_script and Pre-reboot Dexopt.

Pre-reboot Dexopt uses this pipe to check if otapreopt_script is alive,
and cancels itself when otapreopt_script dies.

Bug: 311377497
Test: -
  1. system/update_engine/scripts/update_device.py out/dist/aosp_cf_x86_64_phone-ota-*.zip
  2. Wait for update_engine to enter the postinstall stage.
  3. adb shell update_engine_client --cancel
Change-Id: I9ef4525f4d0b3b8344604166a044c9e3e1bf18a0