OTP import: support hash names with HMAC- prefix
    
    Refactor convertHashName() method to accept hash names prefixed with
    HMAC- or any other prefix. Extending the method should be easier in
    future.
    
    Add tests proposed by Rob Crittenden to make sure we don't regress
    with expected behavior of convertHashName().
    
    Fixes https://pagure.io/freeipa/issue/7146
    
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>