[SPARK-4057] Use -agentlib instead of -Xdebug in sbt-launch-lib.bash for debugging

[sarutak]

In -launch-lib.bash, -Xdebug option is used for debugging. We should use -agentlib option for Java 6+.

[SparkQA]

QA tests have started for PR 2904 at commit 26b4af8.

• This patch merges cleanly.

[SparkQA]

QA tests have finished for PR 2904 at commit 26b4af8.

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

[srowen]

+1 I can confirm that -Xdebug went away in Java 5 I think and this is the modern invocation of the debugger.

[SparkQA]

Test build #22664 has finished for PR 2904 at commit 39b5320.

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

[JoshRosen]

It looks like this file comes from the sbt-launcher-package project. This change seems reasonable to me; do you mind opening an upstream pull request so that the SBT maintainers can take a look at this and sign off? This would also ensure that we don't accidentally revert this change if we decide to pull in a newer version of the launcher scripts.

[sarutak]

@JoshRosen Thanks for notification!
I've opened the PR at the project.
sbt/sbt-launcher-package#83

I'll wait for merging that PR.

[pwendell]

The upstream change was merged so I can pull this in now.