Add support for --module=mod to bin/setup-dunepy.py

This adds an optional parameter --module=mod to setup-dunepy.py. If this parameter is passed, only mod and its dependencies are used as dependencies of the newly created dune-py module. This allows to do

dunecontrol --opts=my.opts --module=foo all
setup-dunepy.py --opts=my.opts --module=foo install

which would otherwise fail if setup-dunepy.py tries to process found modules that have not been build by dunecontrol. If the option is not passed all found modules are used as dependencies as before.