CI tests not working in other repositories
.gitlab-ci.yml currently sets
INTEGRATION_CACHE to the absolute path /builds/BuildStream/buildstream/cache/, which is the
cache subdirectory of the working directory of the CI runner. However, the absolute path of the working directory depends on the URL of the repository, which means that CI tests no longer work in copies/forks of the main repository. We should fix
.gitlab-ci.yml such that it doesn't rely on absolute paths.
Example of error message:
PermissionError: [Errno 13] Permission denied: '/builds/BuildStream'