Ensure we disable tenant isolation without admin

This commit fixes an issue with the tempest configuration when
TEMPEST_HAS_ADMIN is disabled. Without admin credentials tempest
is unable to create credentials at all so enabling tenant isolation
is not going to work. Previously devstack wasn't setting it one way
or the other when TEMPEST_HAS_ADMIN was set, which results in the
default of being enabled. So jobs that try to run tempest without
admin were failing.

Change-Id: Iff496cb5cbf29f17c130cfad746b48d8547ca965
diff --git a/lib/tempest b/lib/tempest
index 10dd652..bd76be5 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -564,9 +564,13 @@
         fi
         iniset $TEMPEST_CONFIG auth allow_tenant_isolation False
         iniset $TEMPEST_CONFIG auth test_accounts_file "etc/accounts.yaml"
+    elif [[ $TEMPEST_HAS_ADMIN == "False" ]]; then
+        iniset $TEMPEST_CONFIG auth allow_tenant_isolation ${TEMPEST_ALLOW_TENANT_ISOLATION:-False}
+
     else
         iniset $TEMPEST_CONFIG auth allow_tenant_isolation ${TEMPEST_ALLOW_TENANT_ISOLATION:-True}
     fi
+
     # Restore IFS
     IFS=$ifs
 }