* #524: Add testrun_uid fixture. This is a shared value that uniquely identifies a test run among all workers. This also adds a PYTEST_XDIST_TESTRUNUID environment variable that is accessible within a test as well as a command line option --testrunuid to manually set the value from outside. OBS-URL: https://build.opensuse.org/package/show/devel:languages:python:pytest/python-pytest-xdist?expand=0&rev=15