Tempest: Fix DeprecationWarning for Read-only property

The following Read-only property has moved in Pike [1].
    os_adm -> os_admin
    os -> os_primary

[1] I9f7c13da05a8c4a63529c11aa6213a7269abee6d
    Ie4cf457d0a521910a82e41e7dad775df75d56587

Change-Id: I512048211888c3db40f95a084164e3add47e3588
diff --git a/neutron/tests/tempest/api/base.py b/neutron/tests/tempest/api/base.py
index 84746fb..10e3559 100644
--- a/neutron/tests/tempest/api/base.py
+++ b/neutron/tests/tempest/api/base.py
@@ -90,7 +90,7 @@
     @classmethod
     def setup_clients(cls):
         super(BaseNetworkTest, cls).setup_clients()
-        cls.client = cls.os.network_client
+        cls.client = cls.os_primary.network_client
 
     @classmethod
     def resource_setup(cls):
@@ -428,8 +428,8 @@
     @classmethod
     def setup_clients(cls):
         super(BaseAdminNetworkTest, cls).setup_clients()
-        cls.admin_client = cls.os_adm.network_client
-        cls.identity_admin_client = cls.os_adm.tenants_client
+        cls.admin_client = cls.os_admin.network_client
+        cls.identity_admin_client = cls.os_admin.tenants_client
         cls.identity_admin_clientv3 = cls.os_admin.projects_client
 
     @classmethod