This job requires two CI variables set
COVERITY_SCAN_TOKEN set in the environment (e.g. schedule). The former's value is project name (in our
case most notably the branch on which this job is executed - e.g.
bind-master), the latter is it's token.
Coverity Scan tools are expected to be in the image, see https://gitlab.isc.org/isc-projects/images/merge_requests/15.