Fix deb and rpm classifier syntax

Author: breskeby

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/distribution/DebElasticsearchDistributionType.java

@@ -25,6 +25,6 @@ public String getName() {
 
     @Override
     public String getClassifier(ElasticsearchDistribution.Platform platform, Version version) {
-        return Architecture.current().debianClassifier;
+        return ":" + Architecture.current().debianClassifier;
     }
 }

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/distribution/RpmElasticsearchDistributionType.java

@@ -35,6 +35,6 @@ public boolean isDocker() {
 
     @Override
     public String getClassifier(ElasticsearchDistribution.Platform platform, Version version) {
-        return Architecture.current().bwcClassifier;
+        return ":" + Architecture.current().bwcClassifier;
     }
 }