Only set the custom https agent for HTTPS minio

Otherwise, we get a Cannot set property ‘agent’ of undefined error

src/storage/s3.js

@@ -108,7 +108,7 @@ function getS3Config(apiConfig, callback) {
 
     if (apiConfig.endpoint) credentials.endpoint = apiConfig.endpoint;
 
-    if (apiConfig.acceptSelfSignedCerts === true) {
+    if (apiConfig.acceptSelfSignedCerts === true && credentials.endpoint && credentials.endpoint.startsWith('https://')) {
         credentials.httpOptions.agent = {
             agent: new https.Agent({ rejectUnauthorized: false })
         };