Test that is-running will exit fast if stuff is running elsewhere

[brendanheywood]

• tab 1: run cron.php
• tab 2: run time cron.php --is-running it should exit within a second or so

[kenneth-hendricks]

tab 1: sudo -u www-data php admin/cli/cron.php --enable
tab 1: sudo -u www-data php admin/cli/cron.php

tab 2: sudo -u www-data php admin/cli/cron.php --is-running

-- should exit fast and display Cron is running