[rackspace|compute] fixes chef bug #1492

This should address bug #1492 which is preventing chef from creating Rackspace Servers with Fog 1.9.0.

@brianhartsock @bradgignac - Could you guys review please? Thanks!

@geemus Due to the major impact of this bug on chef users, would it be possible to cut another release after this commit is accepted?

Thanks!