[2888] Try connecting instead of looking for socket file

This should solve the race condition when the socket file is created,
but connect to it does not work yet, because listen() was not called on
it yet. Really connecting ensures it is possible to connect.

src/bin/msgq/tests/msgq_run_test.py

@@ -72,12 +72,21 @@ class MsgqRunTest(unittest.TestCase):
         # Start msgq
         self.__msgq = subprocess.Popen([MSGQ_PATH, '-s', SOCKET_PATH],
                                        close_fds=True)
-        # Wait for it to become ready (up to the alarm-set timeout)
-        while not os.path.exists(SOCKET_PATH):
-            # Just a short wait, so we don't hog CPU, but don't wait too long
-            time.sleep(0.01)
         # Some testing data
         self.__no_recpt = {"result": [-1, "No such recipient"]}
+        # Wait for it to become ready (up to the alarm-set timeout)
+        connection = None
+        while not connection:
+            try:
+                # If the msgq is ready, this'll succeed. If not, it'll throw
+                # session error.
+                connection = isc.cc.session.Session(SOCKET_PATH)
+            except isc.cc.session.SessionError:
+                time.sleep(0.1) # Retry after a short time
+        # We have the connection now, that means it works. Close this
+        # connection, we won't use it. Each test gets enough new connections
+        # of its own.
+        connection.close()
 
     def __message(self, data):
         """