Pass disable_ssl_certificate_validation to gabbit tests

The patch passes disable_ssl_certificate_validation to gabbi
tests driver.

Change-Id: Ib70341bb0c083d296e074d1cf062bc355ac24432
diff --git a/heat_tempest_plugin/tests/api/test_heat_api.py b/heat_tempest_plugin/tests/api/test_heat_api.py
index 7ba3a62..7ad35c8 100644
--- a/heat_tempest_plugin/tests/api/test_heat_api.py
+++ b/heat_tempest_plugin/tests/api/test_heat_api.py
@@ -92,8 +92,10 @@
             else:
                 register_test_case_id(test_case)
 
+    cert_validate = not conf.disable_ssl_certificate_validation,
     api_tests = driver.build_tests(test_dir, loader, url=endpoint, host="",
                                    fixture_module=fixtures,
+                                   cert_validate=cert_validate,
                                    test_loader_name=__name__)
     register_test_suite_ids(api_tests)
     return api_tests