On OpenStack#Virtuals Machines:

There was an error listing VMs: Expected([200, 204]) <=> Actual(300 Multiple Choices) excon.error.response :body => "{\"choices\": [{\"status\": \"CURRENT\", \"media-types\": [{\"base\": 
\"application/xml\", \"type\": \"application/vnd.openstack.compute+xml;version=2\"}, {\"base\": \"application/json\", \"type\": \"application/vnd.openstack.compute+json;version=2\"}], \"id\": 
\"v2.0\", \"links\": [{\"href\": \"http://<HisAddress>:8774/v2/v2.0/tenants\", \"rel\": \"self\"}]}]}" :headers => { "Content-Length" => "325" "Content-Type" => "application/json" "Date" => "Mon, 06 
Jul 2015 11:00:35 GMT" } :local_address => "<MyAddress>" :local_port => 34717 :reason_phrase => "Multiple Choices" :remote_ip => "<HisAddress>" :status => 300 :status_line => "HTTP/1.1 300 Multiple Choices\r\n" 

The problem seems to be with Fog 1.32.0, when downgrading to 1.31.0 it seems to work as expected.
The problem w/ fog is the URL it generates: http://<HisAddress>:8774/v2/v2.0/tenants should be http://<HisAddress>:8774/v2.0/tenants