Apache : wrong pid path in alpine images

[dauriata]

For alpine images, It seems that apache pid file is in /var/run/apache2/httpd.pid but here is the pid cleaner found in httpd.sh :

# Apache gets grumpy about PID files pre-existing
rm -f /var/run/httpd/httpd.pid

hence apache enter a boot loop in case of unclean exit
only tested with alpine 7.4
was introduced with this commit 20cb068 to get list of impacted images

linked PR #458