Issue #2171683 by sun, alexpott, tstoeckler, larowlan: Remove all Simpletest overrides and rely on native multi-site functionality instead.

Revert "Issue #2171683 by sun, tstoeckler, larowlan: Remove all Simpletest overrides and rely on native multi-site functionality instead."

This reverts commit 91db25eb. Broke web
tests.

Issue #2171683 by sun, tstoeckler, larowlan: Remove all Simpletest overrides and rely on native multi-site functionality instead.

Issue #2100329 by cosmicdreams: Use \Drupal instead of Drupal to make IDEs and static code analyse tools happy.

Issue #1856766 by chx, Berdir, heyrocker, kim.pepper: Convert file_public_path() to the new settings system (make it not configurable via UI or YAML).

This reverts commit 2d6fdda1.