Added default security group to the OpenStack compute mocks.
OpenStack server creation mock now stores the security groups for the
created server.
OpenStack security group mock deletion now deletes created security
groups.
OpenStack security group mock list now accepts a server id like the real
implementation.
Altered the paths for EC2 credential requests to remove an extra / in
the request URIs.
Altered Fog::Open::Identity::Real#request to retry only once when given
a 401 error response code. The EC2 API returns 401 when attempting to
fetch nonexistent EC2 credentials instead of something sensible like
404, leading to an infinite loop. Also, the "Bad username or password"
check was removed. My version of OpenStack does not return this message
when a token is expired, but returns the same message as for a missing
EC2 credential.
