[rackspace|compute] added attach_volume method to server; cleaned up attachment model
Merge branch 'master' of github.com:fog/fog into volume_actions
[rackspace|compute] made device an optional parameter in attach_volume method and request; split volume_attach and attachments into two different tests
Merge branch 'master' of github.com:fog/fog into volume_actions
Merge pull request #1457 from rackspace/volume_actions

[rackspace|compute] cleaned up attachment model