default the target registry to seedserver:5000

Change-Id: I5dc82b1403a9b3334b8f7a782247e2ad7167385e
diff --git a/build.gradle b/build.gradle
index 3b8f645..b82f55e 100644
--- a/build.gradle
+++ b/build.gradle
@@ -55,7 +55,9 @@
         ? 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')