[Openstack|Tests] Add rake subtask for testing only Openstack
[Openstack|Compute|Server] Add test boot from block_device_mapping
[Openstack|Compute|Server] Add test boot from block_device_mapping_v2
[Openstack|Compute|Server] Rewrite block_device_mapping to support

Old support did not properly handle multiple volume attachments for block_device_mapping_v2
V2 support is much different and should be requested with the proper key name rather than being merged into block_device_mapping
Merge pull request #3323 from brandondunne/fix_block_device_mappings

Fix block device mappings