[Build] Post commit hash with timeout messages

[By request](https://github.com/apache/spark/pull/2588#issuecomment-57266871), and because it also makes sense.

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #2597 from nchammas/timeout-commit-hash and squashes the following commits:

3d90714 [Nicholas Chammas] Revert "testing: making timeout 1 minute"
2353c95 [Nicholas Chammas] testing: making timeout 1 minute
e3a477e [Nicholas Chammas] post commit hash with timeout

dev/run-tests-jenkins

@@ -141,8 +141,10 @@ function post_message () {
   test_result="$?"
 
   if [ "$test_result" -eq "124" ]; then
-    fail_message="**[Tests timed out](${BUILD_URL}consoleFull)** after \
-    a configured wait of \`${TESTS_TIMEOUT}\`."
+    fail_message="**[Tests timed out](${BUILD_URL}consoleFull)** \
+    for PR $ghprbPullId at commit [\`${SHORT_COMMIT_HASH}\`](${COMMIT_URL}) \
+    after a configured wait of \`${TESTS_TIMEOUT}\`."
+
     post_message "$fail_message"
     exit $test_result
   else