bootstrap image: Add remote command execution script

In order to automate the complete bootstrap build process we need a
mechanism to control the second phase which builds the final packages
on the booted bootstrap Haiku. To avoid additional dependencies
(buildbot slave, ssh, rsh,...) we'd have to cross-build, there's now a
pair of simple python scripts that allows executing commands on a remote
machine. The server script (bootstrap_daemon.py) is added to the
bootstrap image and started automatically during the boot.