Add device name to result in devices list.

Fix default and not null constraints on device_name field.

device/datastore.go

@@ -75,7 +75,8 @@ var (
 	last_checkin,
 	dep_profile_status,
 	model,
-	workflow_uuid
+	workflow_uuid,
+	device_name
 	FROM devices`
 )
 

migrations/201606220002_devices_info_up.sql

@@ -1,4 +1,4 @@
 -- Add last_checkin, assume timestamp will be UTC
 ALTER TABLE devices
   ADD COLUMN last_checkin timestamp,
-  ADD COLUMN device_name text;
+  ADD COLUMN device_name text NOT NULL DEFAULT '';