Updates the OpenStack compute server model so that it stores/handles
metadata correctly on Server create again.
This was a regression from 21499d8 (and should properly handle the
concern there too).
Includes an update to the test that fails without these fixes.
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.
