Rename 'hostname' to 'instanceid' in a bunch of places.

There was a fair bit of ambiguity here, where 'hostname' sometimes
meant the i-xxxxx id string and sometimes referred to an actual
name like 'beta-testbox'.  Hopefully this relabeling
will sort things out within this class.

Change-Id: Iff837eb3cd3037e9f5c93a29ecb772de53019633
Clear the host array for each IP.

Previously hostArr was accumulating all hostnames
for all addresses.  If we had two floating IPs for a single
instance then later IPs in the gui claimed to have all the same
fqdns as previous IPs.

Change-Id: Ifc401bc57491d669847897ce9a4b1d338b7ac894