Fix environment detection for Semaphore CI

[browniebroke]

We use semaphore CI with several parallel job and it looks like the environment isn't detected properly currently:

• I couldn't find an environment variable giving the pull request number, (supposed to come from PULL_REQUEST_NUMBER), however I noted SEMAPHORE_BRANCH_ID which is the same ID between builds pushed to the same branch. Example value: 3385909.
• The SEMAPHORE_BUILD_NUMBER is the same across all workers for a given push. It sounds like it should be used as number, not as job. This starts at 1 on each branch, and increases on each push.
• The job ID can be obtained via SEMAPHORE_CURRENT_JOB, and for a given build, each worker will have their own (e.g. 1, 2, 3, etc...). Looking at the config from the other CIs, I think it should be returned as job.

Things I'm not sure about

I don't know if these values are unique enough, or if coveralls expects some of them to be unique project wide.

If more unique values are required, I noted the following other environment variables, which might be useful instead:

• SEMAPHORE_EXECUTABLE_UUID: a uuid value, at least unique per build, but might be per worker
• SEMAPHORE_JOB_UUID: a uuid value, unique per job
• SEMAPHORE_REPO_SLUG: format user/repo in Github

[TheKevJames]

@browniebroke this looks correct to me, at least as a starting point! It might be the case that we want to replace SEMAPHORE_CURRENT_JOB with SEMAPHORE_JOB_UUID, depending on how Semaphore<->Coveralls handles parallel job aggregation, but to be perfectly honest I've never been able to predict that in advance and that always seems to fall to trial and error haha.

Thanks for the contribution! Any chance you have a Semaphore log I could check out where you've built off of this branch?

[browniebroke]

Unfortunately, I can't share the Semaphore log as it's on a private project. I initially had some issues to test it, but I managed to make it work now.

It turns out the changes in this pull request aren't working as they stand, it looks like we're better off using the UUID constants actually. The SEMAPHORE_EXECUTABLE_UUID is unique per build, across workers, and using it instead of SEMAPHORE_BUILD_NUMBER produces better results.

Should be noted that these environment variables are for Semaphore classic. I looked at the docs for Sempahore 2.0 and they seem to be slightly different: https://docs.semaphoreci.com/ci-cd-environment/environment-variables/

[TheKevJames]

This looks great, thanks for the contribution!