Add floating_network_name to heat_plugin

Override default value 'floating_network_name = public'
for heat_plugin

Change-Id: I54301d5164a3d674534ccd668b0104f5408fe531
diff --git a/metadata/service/tempest/init.yml b/metadata/service/tempest/init.yml
index 248cd27..23441dc 100644
--- a/metadata/service/tempest/init.yml
+++ b/metadata/service/tempest/init.yml
@@ -67,6 +67,7 @@
       volume-feature-enabled:
         backup: false
       heat_plugin:
+        floating_network_name: ${_param:runtest_tempest_public_net}
         skip_scenario_test_list: ${_param:runtest_heat_plugin_skip_scenario_test_list}
         skip_functional_test_list: ${_param:runtest_heat_plugin_skip_functional_test_list}
         instance_type: 'm1.tiny_test'