Print friendly message if no floating IPs exist.
Print friendly message if no floating IPs exist.

Fix bug 932071.

Print out a friendly message from nova-manage when the "floating list"
command is issued but no floating IPs have been defined.  Prior to this
change, a generic error message would be printed, pointing to the log
for further details.

Change-Id: I0d11f93e9f51cf4e99e319bc9296f73380564257

n0ano/gantt,n0ano/gantt