You can optionally specify a USERSCRIPTS_DIR volume containing these scripts:
* begin.sh, run at the very beginning
* before.sh, run after the syncing and patching, before starting the builds
* pre-build.sh, run before the build of every device
* post-build.sh, run after the build of every device
* end.sh, run at the very end
Each script will be run in $SRC_DIR and must be owned and writeable only by root
