Change retry output to warn or debug

[chb0github]

The code for output on a retry attempt is currently an error - it's debatable if it's actually an error or not. In my case, retry is pretty typical and only when all attempts have been tried is it an error.

I propose that this code

			resp, err = r.client.execute(r)
			if err != nil {
				r.client.log.Errorf("%v, Attempt %v", err, r.Attempt)
			}

Be changed to

r.client.log.Warnf

Or

r.client.log.Debugf

So that it can be suppressed unless there is an issue and that when all attempts are tried, then it outputs an Errorf

If this is ok, I will make the change and submit a PR

[jeevatkm]

@chb0github Changed to warn as part of #587 released with v2.8.0