Make 'global' as default location

Author: snehalakshmisha

hydrator-common/src/main/java/io/cdap/plugin/common/Asset.java

@@ -23,7 +23,7 @@
  */
 public class Asset {
 
-  private static final String DEFAULT_LOCATION = "unknown";
+  private static final String DEFAULT_LOCATION = "global";
 
   private final String referenceName;
   private final String fqn;