Create default network for compute rescue tests

server rescue tests also create server without passing
the network to nova which further fail if more than one test network exists.

https://03399ed3bb928f8e37fb-954a4196d912d707c769d8596124df5e
.ssl.cf1.rackcdn.com/720042/1/check/nova-next/ba84dfc/testr_results.html

Change-Id: Ic9930172a1b6937cd038707afd4d0f6e3730efa1
Partial-Bug: #1844568
diff --git a/tempest/api/compute/servers/test_server_rescue.py b/tempest/api/compute/servers/test_server_rescue.py
index 1ac9516..2c1ad80 100644
--- a/tempest/api/compute/servers/test_server_rescue.py
+++ b/tempest/api/compute/servers/test_server_rescue.py
@@ -25,6 +25,7 @@
 
 
 class ServerRescueTestBase(base.BaseV2ComputeTest):
+    create_default_network = True
 
     @classmethod
     def skip_checks(cls):
@@ -106,6 +107,7 @@
 
 
 class ServerStableDeviceRescueTest(base.BaseV2ComputeTest):
+    create_default_network = True
 
     @classmethod
     def skip_checks(self):