Provide wrapper for i.e. project.py with command line overrides
For utilities like project.py which take only a config file, we need to be able to override, i.e., the dataset to cover in the config file; it should run the given config file through a filter that updates given config entries into a new config file, and runs the script with the modified config.
Odataset=xxx - project.py -c foo.xml
should filter foo.xml to make bar.xml which has <dataset>xxx</dataset>
instead of whatever was in foo.xml.