- Quote `${SUBTOOL}` in case it is set but empty
- Add `-e` flag to `grep` so `villas --help` does not show `grep --help`
- Add `-F` flag to `grep` so `villas "[ "` does not show a regexp error
- Don't exit with error when `-h` or `--help` was specified
- Add `-h` and `--help` to `Usage` in the help message.
Signed-off-by: Philipp Jungkamp <philipp.jungkamp@rwth-aachen.de>