Fix "omero admin restart --foreground" (assist #12467).

This PR fixes two issues from the ticket (https://trac.openmicroscopy.org.uk/ome/ticket/12467):
- whitespace in the output of ``bin\omero admin start -h``,
- error on ``bin\omero restart --foreground``.

To test:
- see if ``bin\omero restart --foreground`` and ``bin\omero restartasync --foreground`` work (with a running and stopped server),
- see if the help text for ``restart``, ``restartasync``, ``start`` and ``startasync`` makes sense (the shorter form of the parameter description).