Run time option to attach test container to an existing docker network

Change-Id: I3dc84341eacf724eff762672370925cb6171d2f8
diff --git a/src/test/utils/TestManifest.py b/src/test/utils/TestManifest.py
index 74a95f6..fdd35ee 100644
--- a/src/test/utils/TestManifest.py
+++ b/src/test/utils/TestManifest.py
@@ -35,7 +35,7 @@
             self.start_switch = args.start_switch
             self.image_prefix = args.prefix
             self.onos_image = args.onos
-            self.docker_network = None
+            self.docker_network = args.network if args.network else None
             self.iterations = None
             self.server = '{}:{}'.format(CORD_TEST_HOST, CORD_TEST_PORT)
             self.jvm_heap_size = args.jvm_heap_size if args.jvm_heap_size else None