Change the way we handle record updates.

When a node goes live, the PDNS Listener will try to insert a record
into PDNS. If the IP already has a record, but there's no record for
hostname, currently it'll just do nothing.

This update will nuke the IP record,and create a new record in its place
with the correct information.
nuke old records and replace them on node register
removed redundant check and verified that we aren't setting records for localhost
A few changes:

- Change the "don't create records for servers with tun interfaces" to
  also include docker interfaces, and only trigger if there's no
  hostname record already. If it does trigger, create an event.

- Create an event if the IP of a record gets updated.

- If there's already a record for the IP we're using, but not one for
  the hostname, nuke the old record and replace it.
Merge pull request #110 from optopus/pdns/update

Pdns/update