The CAS uses a temp directory while manipulating the cache, temporary
files can be added and removed while adding artifacts to the cache here.

Since calculation of the cache size happens in parallel to artifact
cache additions, this causes race conditions in the size calculation
job, as we end up calling `stat` on temporary files which are being
removed in parallel.

Handle this by moving the temporary directory out of the way, and avoid
considering the tmp directory when calculating the cache size

.gitlab-ci.yml: Remove unused script "install.sh"

See merge request BuildStream/buildstream!617

Python 3.7 support

See merge request BuildStream/buildstream!615

Do not rely on `StopIteration` bubbling up.

https://www.python.org/dev/peps/pep-0479/

This reverts commit 4f168b9b6a02216e2fae24d758ae6b778e545869.

The latest version of pytest_pylint works fine with pylint 2, which
means there is no longer a reason to restrict the pylint version.

pylint 2 is required for Python 3.7.

Add warning to git track if track and ref are not present

Closes #471

See merge request BuildStream/buildstream!580

This is to address https://gitlab.com/BuildStream/buildstream/issues/471 that
documented unhelpfull behavour when tracking git sources.

Change install instructions for python-arpy package on Arch

See merge request BuildStream/buildstream!614

  - python-arpy is unobtainable via pacman
  - Also a minor change to how we display install instructions
  from Fedora's dnf package manager