Rate limit jar collection processing

[jack-berg]

Jar collection processing can use high amounts of CPU at application startup. We should adjust the code to rate limit this process and effectively draw out jar processing over a longer period of time.

A rudimentary version of this strategy is available in this branch: https://github.com/newrelic/newrelic-java-agent/compare/rate-limit-jar-collector

Ideally the allowable rate would have a reasonable default, but also be configurable.