[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
Reinstate Rackspace "bin" checks

Following v1.25.0, Rackspace support was extracted into a module however
it broke support to the original fog API.

The Rackspace module is currently disabled until a few key files are
replaced.

This adds tests that worked against v1.25.0 that checks that `rackspace`
is registered correctly. See https://github.com/fog/fog/pull/3326

This reverts commit 9717002fd3d18aef0c359fc52ac704894a34dac0.
Revert "Moving Rackspace logic to fog-rackspace"

This reverts commit d6ecb19d24503d432d84042753afa1304648d055.

Conflicts:
	fog.gemspec
[digitalocean|compute] add private_networking attribute
[digitalocean] reenable tests

closes #3330
Merge pull request #3323 from brandondunne/fix_block_device_mappings

Fix block device mappings
Merge pull request #3331 from rackspace/reinstate_rackspace

Revert "Moving Rackspace logic to fog-rackspace"
More specs to cover `Fog` methods
Merge pull request #3329 from fog/reinstate_rackspace

Reinstate Rackspace support
Merge pull request #3334 from fog/more_abstraction_specs

More specs to cover `Fog` methods