create default network for few more server tests

Below tests are failing on multiple network found

- ServersAdminTestJSON
- ImagesOneServerTestJSON

https://b5afffe3af714f1125c3-25f3a3879427e395d97921f59eb3db3c.ssl.cf2.rackcdn.com/882316/1/gate/nova-next/3a53c36/testr_results.html

creating the default network for those test to make
sure we create and pass the isolated networkin server
create requests.

Partial-Bug: #1844568
Change-Id: I6ab630fb2cd77c9de7dcf93c02a31ff2bcdf03a1
diff --git a/tempest/api/compute/admin/test_servers.py b/tempest/api/compute/admin/test_servers.py
index bc00f8c..321078c 100644
--- a/tempest/api/compute/admin/test_servers.py
+++ b/tempest/api/compute/admin/test_servers.py
@@ -25,6 +25,8 @@
 class ServersAdminTestJSON(base.BaseV2ComputeAdminTest):
     """Tests Servers API using admin privileges"""
 
+    create_default_network = True
+
     @classmethod
     def setup_clients(cls):
         super(ServersAdminTestJSON, cls).setup_clients()
diff --git a/tempest/api/compute/images/test_images_oneserver.py b/tempest/api/compute/images/test_images_oneserver.py
index 23f8326..2b859da 100644
--- a/tempest/api/compute/images/test_images_oneserver.py
+++ b/tempest/api/compute/images/test_images_oneserver.py
@@ -24,6 +24,8 @@
 class ImagesOneServerTestJSON(base.BaseV2ComputeTest):
     """Test server images API"""
 
+    create_default_network = True
+
     @classmethod
     def resource_setup(cls):
         super(ImagesOneServerTestJSON, cls).resource_setup()