EC2-API: Fix ambiguous ipAddress/dnsName issue

Currently, the public ipAddress and dnsName take in either the
fixed or floating IP address as a value. The current fix ensures
that the public dnsName and the public ipAddress both get only
the floating ip address. A look into Amazon's EC2 API Reference
tells us that if there is no public IP associated with an instance,
an empty value is returned for <dnsName> and the key <ipAddress>
itself is never returned. This was tested with euca2ools.
Also, the key <publicDnsName> has been removed since it is
the same as <dnsName>

Fixes: bug #1096468

Change-Id: I3b3e3b3f815df41d1976444d33604363e64a7709
Merge "EC2-API: Fix ambiguous ipAddress/dnsName issue"