No error kind returned when network connection not available

If you attempt to install a snap without a network connection you get an error message without a code. This means a client can't determine the cause of the failure.

$ sudo curl --unix-socket /var/run/snapd.socket http://localhost/v2/snaps/hello-mdeslaur -d '{"action": "install"}'|jq .

{
  "type": "error",
  "status-code": 400,
  "status": "Bad Request",
  "result": {
    "message": "cannot install \"hello-mdeslaur\": Post https://api.snapcraft.io/v2/snaps/refresh: dial tcp: lookup api.snapcraft.io on 127.0.0.53:53: server misbehaving"
  }
}