At work we have the use-case that several people connect to a large
Linux box to run tests and debug those interactively.
All tests write their state into a global `/tmp` -- e.g. the vde1 socket
and the VMs' state. This leads to conflicts when multiple people are
doing this.
This change tries to use XDG_RUNTIME_DIR before using Python's detection
of a global temp directory: when connecting, this requires a working
user session, but then we get working directories per user. This is
preferable over doing something like `mktemp -d` per run since that
would break use-cases where you want to keep the VMs' state across
multiple sessions (`--keep-vm-state`).
59b4d0de90