Use tempfile for caching test image
Random suffixes for test resources in setup

This is needed to avoid conflicts in case of faults during reset. Resources
created by subsequent setups will not conflict with resources from previous
setup runs.
Correct handling of lists of ip addresses

If Nova API returns a list of ip addresses in 'cidr' field of network dict, use
netaddr.IPSet to create range from the list. Otherwise, pass the list 'as is'.