Introduce COMPACT_INDEX_POOL env var to limit compact index thread pool

[vs-adm]

This is a quick proposition to fix #6322 using ENV var COMPACT_INDEX_POOL

[ghost]

Thanks for opening a pull request and helping make Bundler better! Someone from the Bundler team will take a look at your pull request shortly and leave any feedback. Please make sure that your pull request has tests for any changes or added functionality.

We use Travis CI to test and make sure your change works functionally and uses acceptable conventions, you can review the current progress of Travis CI in the PR status window below.

If you have any questions or concerns that you wish to ask, feel free to leave a comment in this PR or join our #bundler channel on Slack.

For more information about contributing to the Bundler project feel free to review our CONTRIBUTING guide

[colby-swandale]

Thanks for opening the PR and helping improve Bundler but we cannot accept this. We have a particular way handling configuration that uses ENV vars, see bundle config. And i don't believe this is the appropriate fix either. The issue with the linked ticket is that there is a bug in the compact index that is preventing it from handling the case of not having enough threads available. This will have to be fixed.

[vs-adm]

This is just starting point. I have no idea how to get remaining thread count on limited systems. But I can rewrite code to utilize the common way of handling ENV vars