In addition, the new source image is not a "latest" image, which
is a more unstable tag.

This commit adapts the run.sh to the new version of the
mattrayner/lamp:latest-1604 image that has updated PHP to version 7,
breaking the php.ini edition in the run.sh.

In order to follow the same philosophy as the original image we
define a default value for PHP_DISPLAY_ERRORS in the Dockerfile