Retrieve core-for-system-modules.jar for public and module-lib APIs

Updates the update_prebuilts.py script to retrieve the
core-for-system-modules.jar file for the public and module-lib APIs
from the specified build target when updating the platform (-p). It
will fail if the files do not exist on the server.

Bug: 204189791
Test: ./update_prebuilts.py -p 7862434 --sdk_target sdk_phone_armv7-sdk
      - fail as the file is missing.
      ./update_prebuilts.py -p --sdk_target sdk_phone_armv7-sdk 7875967
      - works
Change-Id: I529134dfaddf36cbce0a155380ef9b272e1f46c0
1 file changed