In case of grep not matching any line, it would return an error code
and thus stop the script. This patch sets "present_boxes" to an empty
value in case any of the commands fail.
* Test CentOS 7 in CI
* Drop support for CentOS, test on Rocky and Debian
* Fix reset playbook for Rocky Linux
* Fix typo
* Disable firewalld during testing
Co-authored-by: Techno Tim <timothystewart6@gmail.com>