Correct 'list index out of range' in FloatingIPDetailsTestJSON

In FloatingIPDetailsTestJSON's resource_setup, 3 floating_ips
are created and appended to cls.floating_ip, but if
create_floating_ip failes, cls.floating_ip will be an empty list,
so in resource_cleanup we should not use 'range(3)', but should
iterate each item in cls.floating_ip.

Closes-Bug: #1632581

Change-Id: I24979f27305c75474825f8ecef2ed56b7171158e
1 file changed