Add support for automatic reruns

[davehunt]

The pytest-rerunfailures plugin automatically reruns failed tests. We should include the reruns in the HTML report, including any debug information. This can help to identify if persistent failures are failing in a consistent manner. Each rerun should have its own row similar to failure but the status should be orange. The total number of reruns should be reported in the summary. Note that due to pytest-dev/pytest#1193, if pytest-xdist is used, reruns will not be included in the report.