THRIFT-4515: cross server test improvement: graceful test server shutdown

This closes #1509
diff --git a/test/crossrunner/util.py b/test/crossrunner/util.py
index e2d195a..c214df8 100644
--- a/test/crossrunner/util.py
+++ b/test/crossrunner/util.py
@@ -20,6 +20,10 @@
 import copy
 
 
+def domain_socket_path(port):
+    return '/tmp/ThriftTest.thrift.%d' % port
+
+
 def merge_dict(base, update):
     """Update dict concatenating list values"""
     res = copy.deepcopy(base)