No tests with Spark in build pipeline

[mkopec87]

Tests from 'test_spark_histogrammar.py' are not executed as part of build pipeline.

[mbaak]

Yes. I've learned by now that this is possible. (We turn the spark tests on for entitymatching as well.)
I'll fix this (= will ask Simon how to do this) when your PR is in.

[mbaak]

I will follow up with this.

[mbaak]

Resolved with:
#68