Numerous boards are failing with the error message "Failure: Autotest client terminated unexpectedly: DUT rebooted during the test run."

https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/testDetails?testName=security_SandboxLinuxUnittests&suite=bvt-inline&daysBack=7&board=&architecture=&boardFamily=&buildConfig=&reason=+Autotest+client+terminated+unexpectedly%3A+DUT+rebooted+during+the+test+run.&version=&milestone=70&dut=&token=ALuFCnRwrkiB96uhSyFf-AGSsJKI%3A1533588813060