Streaming log for notebook job execution

[edwardps]

Problem

Currently, the notebook job execution log can be downloaded after the job completion. For long running notebook job, this requires user to wait until job is completed. While the job is running, there is no visibility into the progress details of the job other that status showing as in-progress.

Proposed Solution

Support streaming log function for execution engines. In doing this, user could get more real-time visibility into the notebook job execution, so that user could have more details to make decision, for example continue to wait for job completion or stop the job immediately.