Fix fixed_network bug 1439634

fixed_networks only verified if tenant isolation is enabled
that does not account for the case of force tenant isolation,
where an isolated tenant will be available regardless of the
tenant isolation default setting.

Closes-bug: #1439634
Change-Id: I8804d46df7f13ad67ef7260803febe444662e9d1
diff --git a/tempest/common/fixed_network.py b/tempest/common/fixed_network.py
index b06ddf2..b533898 100644
--- a/tempest/common/fixed_network.py
+++ b/tempest/common/fixed_network.py
@@ -15,6 +15,7 @@
 
 from tempest_lib import exceptions as lib_exc
 
+from tempest.common import isolated_creds
 from tempest import config
 from tempest import exceptions
 
@@ -38,7 +39,7 @@
     network = None
     # NOTE(andreaf) get_primary_network will always be available once
     # bp test-accounts-continued is implemented
-    if (CONF.auth.allow_tenant_isolation and
+    if (isinstance(creds_provider, isolated_creds.IsolatedCreds) and
         (CONF.service_available.neutron and
          not CONF.service_available.ironic)):
         network = creds_provider.get_primary_network()