remove *.static.cloud-ips.com

Rackspace no longer sets the reverse dns for cloud servers as the spin
up.

https://community.rackspace.com/general/f/34/t/623
Merge branch 'master' of github.com:gtmanfred/ohai
[OHAI-518] remove *.static.cloud-ips.com

Fixes issues with Pull Request #215
- fixes tests
- moves `require "resolve"` to top of file
Catch specific Resolv exceptions when getting hostname for rackspace.
Stub out and test Resolv exceptions for rackspace hostname attribute.
Splitting Resolv exception test into multiple tests.

The code was taken from an example given by Bryan McLellan.
This adds a Resolv stub to the top scope for all the tests.
Merge pull request #345 from squaresurf/pr-215-fix

[OHAI-518] remove *.static.cloud-ips.com