revert change for default user:group, keep default at oracle:oracle

Author: ddsharpe

imagetool/src/main/java/com/oracle/weblogic/imagetool/util/DockerfileOptions.java

@@ -79,9 +79,6 @@ public DockerfileOptions(String buildId) {
         updateOpatch = false;
         skipJavaInstall = false;
 
-        username = "oracle";
-        groupname = "root";
-
         javaHome = DEFAULT_JAVA_HOME;
         oracleHome = DEFAULT_ORACLE_HOME;
         domainHome = DEFAULT_DOMAIN_HOME;