default the target registry to seedserver:5000

Change-Id: Ie3073b9af74d9fb8622b4621880afd4e38bab48e
diff --git a/build.gradle b/build.gradle
index da1440f..c13f57d 100644
--- a/build.gradle
+++ b/build.gradle
@@ -53,7 +53,9 @@
         ? project.getProperty('targetReg')
         : config.docker && config.docker.registry
             ? config.docker.registry
-            : 'localhost:5000'
+            : config.seedServer.ip
+                ? config.seedServer.ip + ":5000"
+                : 'localhost:5000'
 
     // The tag used to tag the docker images push to the target registry
     targetTag = project.hasProperty('targetTag')