Update buildbot-build.sh to support prebuilts libartpalette-system.

The script will replace the stub in the out directory with the
implementation fetched from the build server.

Test: buildbot-build.sh --target, buildbot-build.sh --host
Bug: 142935992
Change-Id: If2aec5dad404c63d212412afa777a204ee6319c2
1 file changed