suites: Wait for BTS to connect to BSC before continuing

Change-Id: I027e3bfb8f470a811e65e718e2a8c46809fe6396
diff --git a/suites/gprs/ping.py b/suites/gprs/ping.py
index f6f01a6..1b6d85c 100755
--- a/suites/gprs/ping.py
+++ b/suites/gprs/ping.py
@@ -27,6 +27,7 @@
 bsc.start()
 
 bts.start()
+wait(bsc.bts_is_connected, bts)
 print('Waiting for bts to be ready...')
 wait(bts.ready_for_pcu)
 pcu.start()