Engine: 'start' starts the specified container
httpapi: don't create a pidfile if it isn't set in the configuration
Engine: fix a bug which caused handlers to be shared between multiple engine instances
Engine: don't export private testing utilities
Engine: improved logging and identification of jobs
Engine: optional environment variable 'Logging' in 'serveapi'
Hack: simplify the creation of test directories
Engine: fix a bug when encoding a job environment to json
Better error reporting in engine logs and unit tests