nitb/ctrl: Implement a command to list all active subscribers

This is only useful for small networks. List the IMSI and MSISDN
of all active subscribers.

Fixes: SYS#266
diff --git a/openbsc/tests/ctrl_test_runner.py b/openbsc/tests/ctrl_test_runner.py
index 56e9514..60d90a7 100644
--- a/openbsc/tests/ctrl_test_runner.py
+++ b/openbsc/tests/ctrl_test_runner.py
@@ -341,6 +341,13 @@
         self.assertEquals(r['mtype'], 'ERROR')
         self.assertEquals(r['error'], 'Failed to find subscriber')
 
+    def testSubscriberList(self):
+        # TODO. Add command to mark a subscriber as active
+        r = self.do_get('subscriber-list-active-v1')
+        self.assertEquals(r['mtype'], 'GET_REPLY')
+        self.assertEquals(r['var'], 'subscriber-list-active-v1')
+        self.assertEquals(r['value'], None)
+
 class TestCtrlNAT(TestCtrlBase):
 
     def ctrl_command(self):