cleanup log output while building

there was a [great talk at Devoxx](https://youtu.be/2HyGxtsDf60) this year concerning log output while building (besides some other interesting facts). actually it reminded me of the problem we had when hitting Travis-CI max i/o size. If we log less/disable log output we would prevent unnecessary failing builds. in addition, the build time would surely increase.
what do you guys think about it?

The issue names no files or build entry points; start by reviewing the project's build configuration and Travis-CI job output to locate the excessive logging. Compare the current output with the Travis-CI I/O limit and clarify which logs may be reduced before defining a measurable completion condition.

Written by the indexing model from the issue text.