Update getting-started-compute.md

Extended my comments and the normalised server status. On Openstack, server.STATUS.active is not available... In Horizon, this is the Instance Power State, as opposed to the instance status, which is stored in server.openstack.OS-EXT-STS:vm_state , as far as I can figure it out...
I have to admit, I am just starting to look into this (both OpenStack and pkgcloud), so if there are any obvious 'DOH's in what I am writing, be patient ;-)
One of my ideas at at the moment is to write a "set up your DevStack base config automatically" set of scripts, will share if I manage to create anything useful there...