Don't fail to register introspection rules when variable is None

ansible/group_vars/all/inspector

@@ -58,7 +58,7 @@ inspector_ipmi_password: "{{ ipmi_password }}"
 
 # Ironic inspector default network interface name on which to check for an LLDP
 # switch port description to use as the node's name.
-inspector_lldp_switch_port_interface_default:
+inspector_lldp_switch_port_interface_default: eth0
 
 # Ironic inspector map from hostname to network interface name on which to
 # check for an LLDP switch port description to use as the node's name.

ansible/overcloud-introspection-rules.yml

@@ -49,6 +49,6 @@
       # These variables may be referenced in the introspection rules.
       inspector_rule_var_ipmi_username: "{{ inspector_ipmi_username }}"
       inspector_rule_var_ipmi_password: "{{ inspector_ipmi_password }}"
-      inspector_rule_var_lldp_switch_port_interface: "{{ inspector_lldp_switch_port_interface_default or '' }}"
+      inspector_rule_var_lldp_switch_port_interface: "{{ inspector_lldp_switch_port_interface_default }}"
       inspector_rule_var_deploy_kernel: "{{ ipa_kernel_id.stdout }}"
       inspector_rule_var_deploy_ramdisk: "{{ ipa_ramdisk_id.stdout }}"

ansible/seed-introspection-rules.yml

@@ -12,6 +12,6 @@
       # These variables may be referenced in the introspection rules.
       inspector_rule_var_ipmi_username: "{{ kolla_bifrost_inspector_ipmi_username }}"
       inspector_rule_var_ipmi_password: "{{ kolla_bifrost_inspector_ipmi_password }}"
-      inspector_rule_var_lldp_switch_port_interface: "{{ kolla_bifrost_inspector_lldp_switch_port_interface or '' }}"
+      inspector_rule_var_lldp_switch_port_interface: "{{ kolla_bifrost_inspector_lldp_switch_port_interface }}"
       inspector_rule_var_deploy_kernel: "{{ kolla_bifrost_inspector_deploy_kernel }}"
       inspector_rule_var_deploy_ramdisk: "{{ kolla_bifrost_inspector_deploy_ramdisk }}"