IamAwsProvider: fix custom endpoint having non-default port (#1523)

Author: jgolda

api/src/main/java/io/minio/credentials/IamAwsProvider.java

@@ -140,6 +140,7 @@ private String fetchImdsToken() {
           new HttpUrl.Builder()
               .scheme(url.scheme())
               .host(url.host())
+              .port(url.port())
               .addPathSegments("latest/api/token")
               .build();
     }
@@ -188,6 +189,7 @@ private HttpUrl getIamRoleNamedUrl(String token) {
           new HttpUrl.Builder()
               .scheme(url.scheme())
               .host(url.host())
+              .port(url.port())
               .addPathSegments("latest/meta-data/iam/security-credentials/")
               .build();
     }