Enhancements to availability zones api - JCLOUDS-582

https://issues.apache.org/jira/browse/JCLOUDS-582
@demobox What about a single method with varargs?
```
protected Server createServerInZone(String zoneId, CreateServerOptions...options) {
...
}
```

I'm fine with any of the above and the varargs version is cleanest but I'm not sure if that is acceptable.  I might push this version up but I can always change it if necessary.