Issue #2975328 by alexpott, Gábor Hojtsy, borisson_: Install profile in settings.php and mismatch check makes re-installs of Drupal hard

Issue #2907728 by Lendude, vaplas, dawehner, jibran, alexpott, Mile23: Installer: Convert system functional tests to phpunit

Issue #2156401 by alexpott, moshe weitzman, tedbow, dawehner, greg.1.anderson, phenaproxima, chris.smith, heddn, balsama, xjm, Mile23, izus, Manuel Garcia, sun, pwolanin, Berdir: Write install_profile value to configuration and only to settings.php if it is writeable

Revert "Issue #2156401 by alexpott, moshe weitzman, tedbow, dawehner, greg.1.anderson, phenaproxima, chris.smith, heddn, balsama, xjm, Mile23, izus, Manuel Garcia, sun, pwolanin, Berdir: Write install_profile value to configuration and only to settings.php if it is writeable"

This reverts commit 480eb82c.

Issue #2156401 by alexpott, moshe weitzman, tedbow, dawehner, greg.1.anderson, phenaproxima, chris.smith, heddn, balsama, xjm, Mile23, izus, Manuel Garcia, sun, pwolanin, Berdir: Write install_profile value to configuration and only to settings.php if it is writeable