Do not exit with os.Exit(1) but using log.Entry().Fatal() instead
* Golang: forward error details
* extend groovy wrapper to provide proper error message
* create closure for error handling
* Golang step metadata: Config aliases for steps
This will ease following scenarios:
* config migration due to step name changes
* re-use of more general config, e.g. `mavenExecute` in `mavenBuild`
* fix CodeClimate finding
* Fix panic if original stage config does not exist yet
