Improve url validation. Fixes gh-873.

Author: OlgaMaciaszek

spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignClientFactoryBean.java

@@ -417,7 +417,7 @@ <T> T getTarget() {
 			if (LOG.isInfoEnabled()) {
 				LOG.info("For '" + name + "' URL not provided. Will try picking an instance via load-balancing.");
 			}
-			if (!name.startsWith("http")) {
+			if (!name.startsWith("http://") && !name.startsWith("https://")) {
 				url = "http://" + name;
 			}
 			else {
@@ -426,7 +426,7 @@ <T> T getTarget() {
 			url += cleanPath();
 			return (T) loadBalance(builder, context, new HardCodedTarget<>(type, name, url));
 		}
-		if (StringUtils.hasText(url) && !url.startsWith("http")) {
+		if (StringUtils.hasText(url) && !url.startsWith("http://") && !url.startsWith("https://")) {
 			url = "http://" + url;
 		}
 		String url = this.url + cleanPath();