Renamed the PublicIp and set it to addresses in instance snippet

As the heat format of the Instance has been changed from AWS to HOT,
the PublicIp attribute is not longer available. A "address" should
be used instead.

Also, the resource name has to be renamed from PublicIp to the
assigned-ip, as it is not necessary public

Change-Id: I9a4e99680939b6e31d47a1f181b92d1878f65a5e
Closes-Bug: #1319135
Merge "Renamed the PublicIp and set it to addresses in instance snippet"