Skip start base class methods as test unit

Related-Prod: PRODX-28748
Change-Id: I72944248f84cb115ec8f0e952c98109f7f791b4b
(cherry picked from commit b36bf9f01ad24b164bd73e7ec03a76f87219929a)
diff --git a/neutron_tempest_plugin/api/test_subnetpool_prefix_ops.py b/neutron_tempest_plugin/api/test_subnetpool_prefix_ops.py
index 2cd4e1f..49cce5b 100644
--- a/neutron_tempest_plugin/api/test_subnetpool_prefix_ops.py
+++ b/neutron_tempest_plugin/api/test_subnetpool_prefix_ops.py
@@ -23,7 +23,7 @@
 SUBNET_NAME = 'smoke-subnet'
 
 
-class SubnetPoolPrefixOpsTestMixin(test_subnetpools.SubnetPoolsTestBase):
+class SubnetPoolPrefixOpsTestMixin(object):
 
     def _compare_prefix_lists(self, list_expected, list_observed):
         expected_set = netaddr.IPSet(iterable=list_expected)
@@ -65,7 +65,8 @@
                                    resp['prefixes'])
 
 
-class SubnetPoolPrefixOpsIpv4Test(SubnetPoolPrefixOpsTestMixin):
+class SubnetPoolPrefixOpsIpv4Test(test_subnetpools.SubnetPoolsTestBase,
+                                  SubnetPoolPrefixOpsTestMixin):
 
     prefixes = ['192.168.1.0/24', '10.10.10.0/24']
     prefixes_to_add = ['192.168.2.0/24']
@@ -80,7 +81,8 @@
                                 'min_prefixlen': cls.min_prefixlen}
 
 
-class SubnetPoolPrefixOpsIpv6Test(SubnetPoolPrefixOpsTestMixin):
+class SubnetPoolPrefixOpsIpv6Test(test_subnetpools.SubnetPoolsTestBase,
+                                  SubnetPoolPrefixOpsTestMixin):
 
     prefixes = ['2001:db8:1234::/48', '2001:db8:1235::/48']
     prefixes_to_add = ['2001:db8:4321::/48']