Role modules: Docs: Fix default value for string list parameters

Fix default values for string list parameters where default is missing
in the DOCUMENTATION section, but is defined in argument_specs.

roles/ipaserver/library/ipaserver_setup_ca.py

@@ -54,6 +54,7 @@ options:
     type: list
     elements: str
     required: no
+    default: []
   domain:
     description: Primary DNS domain of the IPA deployment
     type: str
@@ -182,6 +183,7 @@ options:
     type: list
     elements: str
     required: no
+    default: []
   no_reverse:
     description: Do not create new reverse DNS zone
     type: bool