Do not update /etc/hosts when running from HDD and when it already contains IP and hostname for current nodename

[jurajlutter]

Do not update /etc/hosts when running from HDD and when it already contains IP and hostname for current nodename.

When running from hdd, /etc/hosts is being updated on each run of /lib/svc/method/identity-node with contents of /etc/nodename and its address. Either check whether the record is already present or do not update /etc/hosts when running from HDD at all.