I have the same error as described on Ubuntu but none of the solutions are directly use-able on the file/directories in httpd of CentOS. The two solutions were to source the /etc/apache2/envvars file which I don't casually see in etc/httpd, and start using the apache script which will create the env variables but apachectl start still gave the error from configtest:
/usr/sbin/apachectl configtest
[Mon Jun 04 23:38:14.248931 2018] [core:warn] [pid 81293] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Mon Jun 04 23:38:14.249056 2018] [core:warn] [pid 81293] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
Syntax OK
