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.
Update the OpenStack security group test to support the correct
format for create_security_group responses. This patch
removes the extra [] wrapping the response and makes it so the
real tests run once again.
Also updates the existing Mock for create_security_response so
it handles it properly as well.
