rfemu_amarisoft: handle exception and log event if WS is closed

the WS is closed if the eNB process dies. this patch will log an
event but not stop the experiment.

Change-Id: I0fafc7e38954400540375d51813e96500700f50c
diff --git a/src/osmo_gsm_tester/obj/rfemu_amarisoftctrl.py b/src/osmo_gsm_tester/obj/rfemu_amarisoftctrl.py
index 17aa43a..585166a 100644
--- a/src/osmo_gsm_tester/obj/rfemu_amarisoftctrl.py
+++ b/src/osmo_gsm_tester/obj/rfemu_amarisoftctrl.py
@@ -53,11 +53,15 @@
     def set_attenuation(self, db):
         msg = { "message": "cell_gain", "cell_id": int(self.cell_id), "gain": -db }
         msg_str = json.dumps(msg)
-        self.dbg('sending CTRL msg: "%s"' % msg_str)
-        self.ws.send(msg_str)
-        self.dbg('waiting CTRL recv...')
-        result = self.ws.recv()
-        self.dbg('Received CTRL msg: "%s"' % result)
+        try:
+            self.dbg('sending CTRL msg: "%s"' % msg_str)
+            self.ws.send(msg_str)
+            self.dbg('waiting CTRL recv...')
+            result = self.ws.recv()
+            self.dbg('Received CTRL msg: "%s"' % result)
+        except Exception:
+            log.Error('Error sending CTLR msg to eNB. eNB still running?')
+            pass
 
     def get_max_attenuation(self):
         return 200 # maximum cell_gain value in Amarisoft