transformation CLI: better error reporting

Change-Id: Ia6ac84991674e9ce33371396893cc8f3aa955df1
Reviewed-on: http://gerrit.esdi-community.eu/3182
Tested-by: Jenkins <sitemple@igd.fraunhofer.de>
Reviewed-by: Simon Templer <simon.templer@igd.fraunhofer.de>