While setting the hostname as a FQDN is perfectly valid, in most cases
the expectation is that /etc/hostname holds the short form hostname and
the FQDN is added as a canonical hostname, i.e. as the first column in
/etc/hosts after the local IP address.

This will allow clients to use:

  hostname -f

to get the fqdn and still be able to get the host form hostname by
calling:

  hostname

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

The --short command line option is a bool which requires the --hostname
option and which will toggles writing the short form hostname to
/etc/hostname.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>