chore: improve retry conditions (#177)

This commit adds an extra status code check to the `shouldRetry` method.

Author: pyrooka

src/main/java/com/ibm/cloud/sdk/core/http/RetryInterceptor.java

@@ -186,7 +186,7 @@ protected int getInterval(Response response, Request request) {
  */
  protected boolean shouldRetry(Response response, Request request) {
  // First check the response.
- if (response.code() == 429 || (response.code() >= 500 && response.code() != 501)) {
+ if (response.code() == 429 || (response.code() >= 500 && response.code() <= 599 && response.code() != 501)) {
  // Now check if we exhausted the max number of retries or not.
  RetryContext context = request.tag(RetryContext.class);
  if (context != null && !context.incCountAndCheck()) {