ofono_client: gracefully handle Scan() failure

ofono's NetworkRegistration.Scan() method fails sporadically. On failure,
check if we are now registered to the desired network, and schedule another
scan otherwise.

For instance it fails with org.ofono.Error.Failed if the modem starts to
register internally after we started Scan() and the registering succeeds
while we are still waiting for Scan() to finsih.

Change-Id: I4a2265ee39a94daa00f525b1c7037a6775509425
diff --git a/src/osmo_gsm_tester/ofono_client.py b/src/osmo_gsm_tester/ofono_client.py
index 67659e1..138f7df 100644
--- a/src/osmo_gsm_tester/ofono_client.py
+++ b/src/osmo_gsm_tester/ofono_client.py
@@ -385,6 +385,7 @@
         netreg = self.dbus.interface(I_NETREG)
         prop = netreg.GetProperties()
         status = prop.get('Status')
+        self.dbg('status:', status)
         if not (status == NETREG_ST_REGISTERED or status == NETREG_ST_ROAMING):
             return False
         if mcc_mnc is None: # Any network is fine and we are registered.
@@ -406,10 +407,21 @@
         # finished.
         register_func = self.scan_cb_register_automatic if mcc_mnc is None else self.scan_cb_register
         result_handler = lambda obj, result, user_data: defer(register_func, result, user_data)
-        error_handler = lambda obj, e, user_data: defer(self.raise_exn, 'Scan() failed:', e)
+        error_handler = lambda obj, e, user_data: defer(self.scan_cb_error_handler, e, mcc_mnc)
         dbus_async_call(netreg, netreg.Scan, timeout=30, result_handler=result_handler,
                         error_handler=error_handler, user_data=mcc_mnc)
 
+    def scan_cb_error_handler(self, e, mcc_mnc):
+        # It was detected that Scan() method can fail for some modems on some
+        # specific circumstances. For instance it fails with org.ofono.Error.Failed
+        # if the modem starts to register internally after we started Scan() and
+        # the registering succeeds while we are still waiting for Scan() to finsih.
+        # So far the easiest seems to check if we are now registered and
+        # otherwise schedule a scan again.
+        self.err('Scan() failed:', e)
+        if not self.is_connected(mcc_mnc):
+            self.schedule_scan_register(mcc_mnc)
+
     def scan_cb_register_automatic(self, scanned_operators, mcc_mnc):
         self.dbg('scanned operators: ', scanned_operators);
         for op_path, op_prop in scanned_operators: