ci: Drop Docker for running tests

Move build steps from Dockerfile to separate script. Run tests directly
in the image via regular GitLab pipeline.
1 job for master in 17 seconds
Status Job ID Name Coverage
  Build
failed #818277
test

00:00:17

 
Name Stage Failure
failed
test Build
Skipping Git submodules setup
Restoring cache
Downloading artifacts
Running before_script and script
$ openshift/docker/build.sh
/bin/bash: line 95: openshift/docker/build.sh: No such file or directory
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1