handle unattached hardware reservations

This is currently failing with:

```
TypeError: 'NoneType' object is not subscriptable
```

Signed-off-by: Adam Bozanich <adam.boz@gmail.com>

Author: boz

packet/HardwareReservation.py

@@ -44,6 +44,12 @@ def __init__(self, data, manager):
         # except (KeyError, IndexError):
         #     self.attached_to = None
 
+
+        # not attached
+        if data["device"] is None:
+            self.attached_to = None
+            return
+
         try:
             device_data = self.manager.call_api(data["device"]["href"], type="GET")
             self.device = Device(device_data, self.manager)