process: respawn(): return process result

Change-Id: Ic6b57b8d0c2993a40ba39b87f45c7a524a8ca440
diff --git a/src/osmo_gsm_tester/process.py b/src/osmo_gsm_tester/process.py
index 4b22d0c..cd125d5 100644
--- a/src/osmo_gsm_tester/process.py
+++ b/src/osmo_gsm_tester/process.py
@@ -205,7 +205,7 @@
         assert not self.is_running()
         self.result = None
         self.killed = None
-        self.launch()
+        return self.launch()
 
     def _poll_termination(self, time_to_wait_for_term=5):
         wait_step = 0.001