Runner script to prevent multiple instances of programs.
Runner script to prevent multiple instances of programs.

This is useful for cron commands that run frequently, but shouldn't
overlap, or to easily create a cron watchdog for services that need to
be kept running.

This is a generalized, and slightly cleaned up, version of code already
used in many infra tools, such as:
svn://svn.chromium.org/chrome-golo/trunk/services/svn/scripts/sync_mirrors.sh

R=agable@chromium.org

Review URL: https://codereview.chromium.org/226463002

nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra