Add check to pr2_computer_monitor to look for hung processes (ros ticket #4982)

[ahendrix]

We should add a check to "cpu_monitor.py" to check for hung processes. Hung processes show up in "dmesg" with a warning like:

{{{
[ 5151.928450] INFO: task iptables:25039 blocked for more than 120 seconds.
[ 5151.928620] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
}}}

We can issue a diagnostic warning or error if we see this message.

trac data:

• Owner: leibs
• Reporter: watts
• Reported at: Tue Jan 18 17:18:48 2011
• URL: https://code.ros.org/trac/wg-ros-pkg/ticket/4982