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_prepare.py

@@ -55,6 +55,7 @@ options:
     type: list
     elements: str
     required: no
+    default: []
   domain:
     description: Primary DNS domain of the IPA deployment
     type: str
@@ -74,6 +75,7 @@ options:
     type: list
     elements: str
     required: no
+    default: []
   no_host_dns:
     description: Do not use DNS for hostname lookup during installation
     type: bool
@@ -114,6 +116,7 @@ options:
     type: list
     elements: str
     required: no
+    default: []
   subject_base:
     description:
       The certificate subject base (default O=<realm-name>).
@@ -134,6 +137,7 @@ options:
     type: list
     elements: str
     required: no
+    default: []
   no_reverse:
     description: Do not create new reverse DNS zone
     type: bool
@@ -149,6 +153,7 @@ options:
     type: list
     elements: str
     required: no
+    default: []
   no_forwarders:
     description: Do not add any DNS forwarders, use root servers instead
     type: bool