`uname -m` is unusable in case of IBM AIX 7 as it reports the serial
number of the machine. As a workaround, special case it and use the
reported processor identifier.

Drop support for `setup.py test`

See merge request BuildStream/buildstream!1758

Drop support for running tests via `setup.py test`, that is considered
deprecated. `tox` is our primary frontend for running tests, so this
change ensures that we don't have to support multiple ways of running
tests.

For testing against a specific installation environment, `tox` is not
quite practical. But in these cases, one can run `pytest` directly. So,
there is no need for this additional indirection.

This was discussed in the following mailing list thread:
https://mail.gnome.org/archives/buildstream-list/2019-December/msg00006.html.

job.py: Do not call Process.close()

Closes #1243

See merge request BuildStream/buildstream!1776

As we handle subprocess termination by pid with an asyncio child
watcher, the multiprocessing.Process object does not get notified when
the process terminates. And as the child watcher reaps the process, the
pid is no longer valid and the Process object is unable to check whether
the process is dead. This results in Process.close() raising a
ValueError.

Fixes: 9c23ce5c ("job.py: Replace message queue with pipe")

setup.cfg: Set pytest default timeout

See merge request BuildStream/buildstream!1775

This sets a default timeout of 15 minutes for tests to avoid hanging
indefinitely.  As the slowest test in CI normally takes less than
5 minutes, the timeout should be long enough to not trigger even on
slower systems if everything operates normally.

buildstream/_platform/platform.py: Add powerpc64 and powerpc64le

See merge request BuildStream/buildstream!1698

Add CI job to test buildbox-run-userchroot

Closes #1237

See merge request BuildStream/buildstream!1751