JCLOUDS-514: Add ability to attach block volumes at boot through the Nova ServerApi

Fixes: https://issues.apache.org/jira/browse/JCLOUDS-514
@demobox As @jasdeep-hundal pointed out, most of the Nova Live Extension API tests follow this pattern, so this should be fine for the time being. In the work I am doing with the `BaseOpenStackLiveApiTest` many of the live tests will be updated.