tools/power turbostat: harden against cpu hotplug

turbostat tends to get confused when CPUs are added and removed
while it is running.

There are races, such as checking the current cpu, and then
reading a sysfs file that depends on that cpu number.

Close the two issues that seem to come up the most.
First, there is an infinite reset loop detector --
change that to allow more resets before giving up.
Secondly, one of those file reads didn't really need
to exit the program on failure...

Signed-off-by: Len Brown <len.brown@intel.com>