fix docker - permission issues and smaller images

[thammegowda]

What changes were proposed in this pull request?

1. Permission issue fixed for sparkler reported in #124
2. Docker build is optimized. The maven build is run in host and then copied to docker. Reasons:
   • to share .m2/repository cache between docker builds
   • To minimize the image size (by excluding all unnecessary files)

Is this related to an already existing issue on sparkler?

124

Will it close an existing issue?
Closes #124

How was this patch tested?

Removed all docker images using docker rmi freshly built docker images.

• previously sparkler user didnt have permissions to edit /data directory, now it has
• previously docker image was > 3GB, now it is 1.8GB
• previously docker used to freshly download all maven deps insider docker. Now maven runs outside (thus reusing .m2 cache) and then copies the final builds inside docker.

[thammegowda]

@buggtb Need your review for this PR.

[buggtb]

I've not tried building but the dockerfile looks good. The only change I would make, and its unrelated to your PR, is set the Ubuntu image to a specific version, :xenial or something so that it doesn't go weird with different Java versions or something when new releases happen.

[thammegowda]

thanks @buggtb