build-doc: fix checks for required commands for non-debian

Fixes: 7695

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #1434 from ceph/wip-7695

build-doc: fix checks for required commands for non-debian

Reviewed-by: Sage Weil <sage@inktank.com>