various minor fix for AbstractLatentBuildSlave and DockerLatentBuildSlave

AbstractLatentBuildSlave:
 - Fix error with build_wait_timeout
DockerLatentBuildSlave: 
 - it doesn't work when max_build!=1 (concurrent build are violently canceled because the container is stopped) => Fix that
 - Fix: Support the build_wait_timeout feature (like all AbstractLatentBuildSlave child class)
 - Fix: remove the last \n of log lines when the docker image is built.
 - Fix: destroy the container when the container is stopped (Container are created on demande, there's no need to keep old container. the disk space will grow up!)
 - Create the container with the slave_name + id. docker ps is easier to read.