[Build] Post commit hash with timeout messages

[nchammas]

By request, and because it also makes sense.

[SparkQA]

QA tests have started for PR 2597 at commit 2353c95.

• This patch merges cleanly.

[SparkQA]

Tests timed out for PR 2597 at commit 2353c95 after a configured wait of 1m.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/21049/

[SparkQA]

QA tests have started for PR 2597 at commit 3d90714.

• This patch merges cleanly.

[SparkQA]

QA tests have finished for PR 2597 at commit 3d90714.

• This patch passes unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/21050/

[nchammas]

cc @rxin

Here is an example of the new timeout message.

[rxin]

LGTM. Merging. Thanks!