Spring XD base image used by other images for single node, multi-node, etc...
This image:
- downloads a Spring XD release from spring.io release repository
- unzips to /opt/spring-xd-${XD_VERSION}
- creates a symbolic link from /opt/spring-xd-${XD_VERSION} to /opt/spring-xd
- makes /opt/spring-xd to working directory
Spring XD is setup to be run as root.