Create module skeleton

Create clean_up{,_process,_database,_filesystem} functions on runbot.repo
Add test skeletons

Create Setup and TearDown
Add skeleton tests for Create clean_up{_process,_database,_filesystem}
Implement cleanup

On database init, mark all builds as done for deletion by the cron

clean_up marks all files in build directory as patterns to be cleaned unless
the build is not done
Implemented clean_up_filesystem method and its test
Implemented clean_up_database method and its test
Implemented clean_up_process method and its test

Add clean_up_pids method which kills done pids