Create default network in volume tests

Volume negative and filter tests create servers without specifying
network, causing the "Multiple possible networks found" exception
when more than one network exists. Enable default network creation
(create_default_network=True) in these tests to avoid this error.

Related-prod: PRODX-51554
Change-Id: I2c836d9e96276b084a1af6d323e4a7775cd2ef13
diff --git a/tempest/api/volume/test_volumes_filters.py b/tempest/api/volume/test_volumes_filters.py
index 74ba9cb..7b48f4b 100644
--- a/tempest/api/volume/test_volumes_filters.py
+++ b/tempest/api/volume/test_volumes_filters.py
@@ -24,6 +24,9 @@
 
 
 class VolumesFilter(base.BaseVolumeAdminTest):
+
+    create_default_network = True
+
     @testtools.skipUnless(
         "InstanceLocalityFilter" in CONF.volume.scheduler_default_filters,
         "Cinder InstanceLocalityFilter is disabled",
diff --git a/tempest/api/volume/test_volumes_negative.py b/tempest/api/volume/test_volumes_negative.py
index 0a3a412..edaf7d5 100644
--- a/tempest/api/volume/test_volumes_negative.py
+++ b/tempest/api/volume/test_volumes_negative.py
@@ -30,6 +30,8 @@
 class VolumesNegativeTest(base.BaseVolumeTest):
     """Negative tests of volumes"""
 
+    create_default_network = True
+
     @classmethod
     def resource_setup(cls):
         super(VolumesNegativeTest, cls).resource_setup()