FreeIPABaseModule: Add support for check_mode.

All ansible-freeipa modules should support 'check_mode: yes', but
the support for creating modules with this was absent in the base
class.

This patch adds such support, to use it, 'supports_check_mode=True'
must be passed to the constructor when creating the module object.

plugins/module_utils/ansible_freeipa_module.py

@@ -786,6 +786,10 @@ else:
 
         def _run_ipa_commands(self):
             """Execute commands in self.ipa_commands."""
+            if self.check_mode:
+                self.changed = len(self.ipa_commands) > 0
+                return
+
             result = None
 
             for name, command, args in self.ipa_commands: