Switch to show/hide host_status field in server detail response to non-admins

We would like to have a switch to show/hide the host_status field in the server details response to all users, not just admins. In certain clouds, knowing this information can help normal users understand why their apparently ACTIVE instance is unreachable. Mechanics-wise, this is similar to BZ 1982283, in that it's a tht configurable to tweak Nova policy.