Enhancement of docker mounting config volume

[zhaoyongjie]

Before PR some comments #4, #5

Yongjie, thanks for this PR! a few comments on this update:

I see you installed Spark 2.2, actually Kylin package already has Spark embedded (with v2.1), so don't need to download and expand Spark;
In the docker run, is the "sandbox.hortonworks.com" required? As this image is common (not bind to HDP), can we remove the sandbox in add-host?
Could you please update the readme file to tell user how to use this docker image?
Thanks!

1. remove SPARK from dockerfile
2. add kylin config volume
3. "sandbox.hortonworks.com" is zookeeper broadcast hostname, is a option for zookeeper config.
4. I will update readme soon