Add job status environment variables

What does this MR do?

• Introduces CI_JOB_STATUS environment variable available to jobs.
• Removes BuildRunRuntimeFinished and splits it up into BuildRunRuntimeSuccess and BuildRunRuntimeFailed

Why was this MR needed?

• A dependency for a proposal in gitlab#15603 (run after_script always... it's good to know what the state of the build was).
• Was requested here: gitlab#16579 (closed)

What's the best way to test this MR?

TestBuildJobStatusEnvVars tests that the environment variables for stage and status are updated as a build progresses from running to failed.

go test -run TestBuildJobStatusEnvVars ./executors/shell

What are the relevant issue numbers?

gitlab#16579 (closed)

Will be handy when after_script is always executed: gitlab#15603