Support jUnit xml style reports in start_test.
Support jUnit xml style reports in start_test.

Add --junit-xml argument. When set, start_test calls new script to convert
logfile to junit xml style report. Also add --junit-xml-file argument, which
implies the --junit-xml argument. When --junit-xml-file is set, its value is
passed along to the conversion script as the junit xml output file.

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