Basic ajax lost password

https://github.com/owncloud/core/issues/2926#issuecomment-43311587
https://github.com/owncloud/core/blob/master/lib/private/user/manager.php#L98 can be used to get the user based on uid, then you can use this method to set the password: https://github.com/owncloud/core/blob/master/lib/private/user/user.php#L158