Ubuntu Dockerfile passes incorrect java user preferences path to image

[NCMEC-daavendasora]

Description: java.util.prefs.userRoot should simply point to ${USER_HOME}. Specifying ${USER_HOME}.java/.userPrefs is redundant and causes java.util.prefs.userRoot to be defined as ${USER_HOME}.java/.userPrefs/.java/.userPrefs

Affected Product Version: 6.0.0.1

Steps to reproduce:

1. cd docker-is/dockerfiles/ubuntu/is
2. docker build -t wso2/wso2is:6.0.0-ubuntu --build-arg "WSO2_SERVER_DIST_URL=https://wso2.org/path/to/wso2is-6.0.0.zip" .
3. docker run --name wso2is-6.0.0 --rm -i -t wso2/wso2is:6.0.0-ubuntu
4. docker exec -it wso2is-6.0.0 bash
5. ls -la /home/wso2carbon/.java/.userPrefs/ the output will be:

   drwxr-xr-x 1 wso2carbon wso2 4096 Sep  8 07:04 .
   drwxr-xr-x 1 wso2carbon wso2 4096 Sep  8 06:52 ..
   drwxr-xr-x 3 wso2carbon wso2 4096 Sep  8 07:04 .java

6. ls -la /home/wso2carbon/.java/.userPrefs/.java/.userPrefs/ produces this output:

   drwx------ 2 wso2carbon wso2 4096 Sep  8 07:04 .
   drwxr-xr-x 3 wso2carbon wso2 4096 Sep  8 07:04 ..
   -rw------- 1 wso2carbon wso2    0 Sep  8 07:04 .user.lock.wso2carbon
   -rw------- 1 wso2carbon wso2    0 Sep  8 07:04 .userRootModFile.wso2carbon

Related Issues: #355 Location to store java preferences is not used by Alpine & Centos images