Refactors PHP_DISPLAY_ERRORS configuration variable

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

Dockerfile

 FROM mattrayner/lamp:latest-1604
 
+ENV PHP_DISPLAY_ERRORS Off
 ADD run.sh /run.sh

run.sh

@@ -3,11 +3,8 @@
 VOLUME_HOME="/var/lib/mysql"
 
 sed -ri -e "s/^upload_max_filesize.*/upload_max_filesize = ${PHP_UPLOAD_MAX_FILESIZE}/" \
-    -e "s/^post_max_size.*/post_max_size = ${PHP_POST_MAX_SIZE}/" /etc/php/5.6/apache2/php.ini
-
-if [ "$PHP_DISPLAY_ERRORS" == "On" ];then
-    sed -ri -e "s/^display_errors.*/display_errors = On/" /etc/php/5.6/apache2/php.ini
-fi
+    -e "s/^post_max_size.*/post_max_size = ${PHP_POST_MAX_SIZE}/" \
+    -e "s/^display_errors.*/display_errors = ${PHP_DISPLAY_ERRORS}/" /etc/php/5.6/apache2/php.ini
 
 sed -i "s/export APACHE_RUN_GROUP=www-data/export APACHE_RUN_GROUP=staff/" /etc/apache2/envvars