New ipamodule_base_vars

There are common parameters in all modules like ipaadmin_principal and
ipaadmin_password. As this list of common parameters will be extended
soon, there is a need to reduce the code and documentation duplicates.

A ModuleDocFragment is added to provide the module documentation for the
common parameters. This is used in the modules with
extends_documentation_fragment.

ansible_freeipa_module has additional ipamodule_base_spec and
get_ipamodule_base_vars. ipamodule_base_spec extends argument_spec in
the module and get_ipamodule_base_vars is used to return a dict
containing the common parameters.

utils/ansible-doc-test

@@ -30,9 +30,11 @@ import subprocess
 def run_ansible_doc(role, module, verbose=False):
     playbook_dir, module_path = get_playbook_dir(role, module)
     module_dir = os.path.dirname(module_path)
+    doc_fragments = os.path.dirname(module_path)+"/../doc_fragments/"
 
     command = ["env",
                "ANSIBLE_LIBRARY=%s" % module_dir,
+               "ANSIBLE_DOC_FRAGMENT_PLUGINS=%s" % doc_fragments,
                "ansible-doc",
                "--playbook-dir=%s" % playbook_dir,
                "--type=module",