JCLOUDS-699: Properly deprecate OpenStack Nova zonescoped package

This PR deprecates the `org.jclouds.openstack.nova.v2_0.domain.zonescoped` package in favor of the `org.jclouds.openstack.nova.v2_0.domain.regionscoped` package and provides some other minor cleanup.

JIRA: https://issues.apache.org/jira/browse/JCLOUDS-699
@everett-toews It looks like AvailabiliyZone doesn't exist in the `regionscoped` package. So either this API deliberately uses deprecated code, or we shouldn't use it here at all?