Return nsaccountlock in user-add as boolean
    
    The `nsaccountlock` attribute was being returned as a
    list of string ("TRUE"/"FALSE") instead of a boolean.
    Use the convert function used in `user-find` and `user-mod`
    for consistency, since these commands return the parameter as a boolean.
    
    Fixes: https://pagure.io/freeipa/issue/8743
    Signed-off-by: Antonio Torres <antorres@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>