Fix missing msg argument

The following patch adds a missing 'msg=' syntax. An exception is raised
in ansible if this block is reached during the execution of the module

    TypeError: fail_json() takes exactly 1 argument (2 given)

With the 'msg=' added, you get a more informative error. For example

    msg: No settings provided to update_domain().
Merge pull request #8038 from caphrim007/correct-missing-msg-argument

Fix missing msg argument