Looks like DOCKER_EXEC got lost somewhere along the way, which, in
turn, caused the "coverity" job to fail with
```
$ $DOCKER_EXEC meson cov-build -Dman=false
Command 'meson' not found, but can be installed with:
apt install meson
Please ask your administrator.
```
https://travis-ci.org/github/systemd/systemd/builds/
701705788
env:
- FEDORA_RELEASE="latest"
- TOOL_BASE="/var/tmp/coverity-scan-analysis"
+ - DOCKER_EXEC="docker exec -ti $CONT_NAME"
- DOCKER_RUN="docker run -v $TOOL_BASE:$TOOL_BASE:rw --env-file .cov-env"
# Coverity env variables
- PLATFORM="$(uname)"