Tests: Added only_$TestName command line argument to multiprocess test, to select a single test to run.

test/mp_sync_test.py

@@ -1,5 +1,5 @@
 """
-test for simplest keysync scenario : two device setting up same account
+tests for keysync scenario
 
 Launch it with something like :
 LC_ALL=en_US.UTF-8 \

test/multipEp.py

@@ -327,6 +327,12 @@ def run_manager_action(action):
     return func(*args, **kwargs)
 
 def run_scenario(scenario):
+    for a in sys.argv:
+        if a.startswith("only_") and a != "only_" + scenario.__name__ :
+            print("IGNORING: " + scenario.__name__)
+            return
+    print("RUNNING: " + scenario.__name__)
+
     global handshakes_seen, handshakes_validated, msgs_folders, instances
     instances = OrderedDict()
     with multiprocessing.Manager() as manager: