Enhancements to availability zones api - JCLOUDS-582

https://issues.apache.org/jira/browse/JCLOUDS-582
I'll update the naming and usage to be consistent with the VolumeApiLiveTest, somehow the other way dos look a bit more clean and intuitive.  The getLast() is same as previous comment, this is just a convention that I saw in all live tests and I wanted to follow that precedent.