refactor(retry-forever): splice all but last error on forever retry

Author: mbroadst

lib/retry_operation.js

@@ -27,6 +27,8 @@ RetryOperation.prototype.retry = function(err) {
   var timeout = this._timeouts.shift();
   if (timeout === undefined) {
     if (this._cachedTimeouts) {
+      // retry forever, only keep last error
+      this._errors.splice(this._errors.length - 1, this._errors.length);
       this._timeouts = this._cachedTimeouts.slice(0);
       timeout = this._timeouts.shift();
     } else {