ci: bring back Coverity part 2

It's just a follow-up to https://github.com/systemd/systemd/pull/16266.

Currently the Coverity stage is failing with
```
Starting container systemd-fedora-latest
2db425228e1addbce607c7e47e492a0faef2c2c4e85701c6c239a50de95944eb
Error: No such container: bash
The command "$CI_MANAGERS/fedora.sh SETUP" failed and exited with 1 during .
Your build has been stopped.
```

https://travis-ci.org/github/systemd/systemd/builds/701798193

.travis.yml

@@ -47,6 +47,7 @@ jobs:
       env:
         - FEDORA_RELEASE="latest"
         - TOOL_BASE="/var/tmp/coverity-scan-analysis"
+        - CONT_NAME="coverity-fedora-$FEDORA_RELEASE"
         - DOCKER_EXEC="docker exec -ti $CONT_NAME"
         - DOCKER_RUN="docker run -v $TOOL_BASE:$TOOL_BASE:rw --env-file .cov-env"
           # Coverity env variables