[SPARK-4000][BUILD] Sends archived unit tests logs to Jenkins master

This PR sends archived unit tests logs to the build history directory in Jenkins master, so that we can serve it via HTTP later to help debugging Jenkins build failures.

@pwendell @JoshRosen Please help review, thanks!
The build number is directly accessible from environment variables. [1] I think the PR number information can be useful when reading PR comments via mail.

[1] https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/21889/injectedEnvVars/