Specs for existing `Fog::Bin` interface

Prepartion for fog/fog-core#105
Detailed checks for `Brightbox` class
Merge branch 'master' into 105_provider_registration
Remove Rackspace references until reinstated

Tests were based on v1.25.0 which included Rackspace support. It was
extracted into a module and not correctly referenced so is no longer
present on master.

This commit should be reverted and the specs passing before the next
release.
Merge pull request #3326 from fog/105_provider_registration

Add specs for existing `Fog::Bin` API