[rackspace] setting rackspace_region to nil in default tests to override any settings loaded via Fog.credentials
[linode|dns] avoid passing host to request

see #2248
Merge pull request #2276 from rackspace/default-tests

[rackspace] fixing broken tests
[linode|compute] Avoid passing host to request.

References #2248
Merge pull request #2277 from fnichol/linode-excon-invalid-host-key

[linode|compute] Avoid passing host to request.