ipareplica/tasks/install.yml: Omit forward_policy if not set in ipareplica_test

forward_policy is only set in dns.install_test in ipareplica_test if
setup_dns is enabled. Therefore forward_policy will be ommited in this
case.

roles/ipareplica/tasks/install.yml

@@ -583,7 +583,7 @@
       ### dns ###
       zonemgr: "{{ ipareplica_zonemgr | default(omit) }}"
       forwarders: "{{ ipareplica_forwarders | default([]) }}"
-      forward_policy: "{{ result_ipareplica_prepare.forward_policy }}"
+      forward_policy: "{{ result_ipareplica_prepare.forward_policy if result_ipareplica_prepare.forward_policy is not none else omit }}"
       no_dnssec_validation: "{{ ipareplica_no_dnssec_validation }}"
       ### additional ###
       ccache: "{{ result_ipareplica_prepare.ccache }}"