tests: Replace is_connected() with is_registered()

API was renamed and old name deprecated, let's use it everywhere.

Change-Id: Ic91dddcfd1a5a17c35d15a8a14628b3923229523
diff --git a/sysmocom/suites/debug/interactive.py b/sysmocom/suites/debug/interactive.py
index fa53cc8..3b6a338 100755
--- a/sysmocom/suites/debug/interactive.py
+++ b/sysmocom/suites/debug/interactive.py
@@ -54,7 +54,7 @@
   elif 'wait-registered'.startswith(cmd):
     try:
       for m in modems:
-          wait(m.is_connected, msc.mcc_mnc())
+          wait(m.is_registered, msc.mcc_mnc())
       wait(msc.subscriber_attached, *modems)
     except Timeout:
       print('Timeout while waiting for registration.')