Limit retries in ping gethostbyname

[fedux]

Hi,

I have a local DNS that resolves queries from spine. If its internet conection is lost, then spine retries DNS queries as fast as it cans and the DNS servers uses 100% CPU trying to respond.

This patch limits the retries and introduces a small delay between each retry, giving the DNS time to recover.

[gandalf]

SVN#5740 fixes this. Thanks for the contribution
R.