Feed domain name from hostname fqdn when possible.

[jonathan-orsel]

In some configuration the command domainname didn't return the expected result but the domain can be deducted from the hostname command :

[user@host agent]$ domainname
(none)
[user@host agent]$ hostname
host.domain.name

For that case, a minor change can do the trick.

[jackburton79]

Thank you!