Fix bts.ready_for_pcu() implementation for sysmo and oc2g

osmo-bts.git ae09c8acb4aa93284cdb44f8bbdc14533dc4fa52 modified code to
avoid calling pcu_tx_info_ind() if pcu socket was not connected. Since
osmo-gsm-tester relied on log message sent from within that funtion to
find out whether BTS was able to handle PCUIF connections, that log line
is not printed anymore and hence the function ready_for_pcu() fails to
ever return true.
As a result, gprs tests for sysmo and oc2g bts types always fail with a
timeout.

Other BTS types are not affected (such as osmo-bts-trx) because in there
we simply check whether the osmo-bts process is running.

Change-Id: Ibde4b8b27b8300b4b9197c0f8d82a6ccbf3b0522
diff --git a/src/osmo_gsm_tester/obj/bts_oc2g.py b/src/osmo_gsm_tester/obj/bts_oc2g.py
index 7761ce3..9164827 100644
--- a/src/osmo_gsm_tester/obj/bts_oc2g.py
+++ b/src/osmo_gsm_tester/obj/bts_oc2g.py
@@ -88,7 +88,7 @@
     def ready_for_pcu(self):
         if not self.proc_bts or not self.proc_bts.is_running:
             return False
-        return 'BTS is up' in (self.proc_bts.get_stdout() or '')
+        return 'Started listening on PCU socket' in (self.proc_bts.get_stdout() or '')
 
     def start(self, keepalive=False):
         if self.bsc is None: