Revert "Issue #2228215 by znerol, Berdir: Remove module check in DrupalKernel."

This reverts commit 341b903d05fb1d8cc2137df2543cf784eccfd568.
Issue #2228215 by znerol, Berdir: Remove module check in DrupalKernel.
Issue #2259275 by filijonka, sun, Xano: Rename "DrupalUnitTestBase" to KernelTestBase.