add pre-release tests

[vladak]

It would be useful (in the light of #1993, #2050) to have a test that indexes bigger repository with higher parallelism and various features that are normally disabled by default (esp. renamed files handling). This can be perhaps done in the integration-test build phase in Maven.

[vladak]

Of course, running this on Travis might not buy us much as I only reproduced the issues when running them on Solaris machines with at least 24 CPU cores.