Add middleware_admin_user and middleware_admin_password parameters

The module will create an admin account, which we should really let the user
control.  Expose the credentials as middleware_admin_user and
middleware_admin_password.
add tests for `middleware_admin_user` and `middleware_admin_password`
Merge pull request #84 from richardc/feature/master/middleware_admin_user

add middleware_admin_user and middleware_admin_password errors