Fix hosts file entries - remove duplicates/stale entries

Adds to tasks in the updatehostsfile play that will do the following to
the /etc/hosts file:
* Removes any entries that match the IP of current host, but with a
  different hostname
* Removes any entries that match the hostname of the current host but
  with a different IP

This will prevent duplicate entries and other /etc/hosts file related
strangeness.

Fixes #13