Add Premain-Class attribute

[nickcaballero]

This PR adds premain method and manifest attribute, supporting the installation of the agent via -javaagent= JVM option.

[pivotal-cla]

@nickcaballero Please sign the Contributor License Agreement!

Click here to manually synchronize the status of this Pull Request.

See the FAQ for frequently asked questions.

[pivotal-cla]

@nickcaballero Thank you for signing the Contributor License Agreement!

[pderop]

@nickcaballero ,

Thanks a lot for this PR ! and sorry to only look into it now.

So, I have several comments (some are about problems, while other are about cosmetics)

First, can you please rebase your PR on top of the latest master ?
Also, can you please describe your new feature somewhere in the documentation.

For example, in the Installation section of the quick_start.md, you could add some kind of the following:

If you can't change the application code, you can also activate BlockHound using the -javaagent:<path to BlockHound agent jar> jvm option, something like:

java -javaagent:BlockHound/agent/build/libs/agent.jar -jar my-application.jar

Now, please have a look at the following review, hope you will have time to work on this before we do the next release, let me know

thanks !

[pderop]

I just rebased this PR on top of latest master.

[nickcaballero]

@pderop I've updated the PR with your suggestions! Went with the loadIntegrations approach for the builder, which I think is a lot cleaner.

[pderop]

@nickcaballero ,

thanks a lot for updating the PR 😃,

One last small thing, could you just add a note somewhere in the documentation, please check #297 (review) ?

thanks

[pderop]

thanks for the PR !

+1 from me (I'll update the doc about using the -javaagent in another new PR).

@reactor/core-team , @reactor/netty-team , can someone of you review all this ? thanks.

[pderop]

@nickcaballero, thanks for this PR !
@chemicL, thanks for the review !

I'll change the parameter names of the premain method in another PR, let's merge this one for the moment.