Summary
- centos8-build: use nightly URL to invalidate cache (details)
- centos8: don't download .repo file (details)
- make: add OSMOCOM_REPO_PATH (details)
- make: add OSMOCOM_REPO_TESTSUITE_MIRROR (details)
- centos8-obs-latest: use OSMOCOM_REPO_VERSION (details)
- osmo-*-latest: use OSMOCOM_REPO_VERSION (details)