Improve test failure message for #1390.

Remove flaky test from sbt.

What was happening is memory pressure was causing the classloader to get evicted in the SCala 2.11 code.   I expect this is because parallel collections in Scala 2.11 use weakreferences as well during execution, so for the .par method, there was no strong reference to any classloader.

Still this is super odd, but if the classloader *IS* collected, it's not the end of the world, nor is it a bug, so the test can disappear.