x/tools/cmd/stress: add utility for stress testing
x/tools/cmd/stress: add utility for stress testing

The stress utility is intended for catching of episodic failures.
It runs a given process in parallel in a loop and collects any failures.
Usage:
 	$ stress ./fmt.test -test.run=TestSometing -test.cpu=10
You can also specify a number of parallel processes with -p flag;
instruct the utility to not kill hanged processes for gdb attach;
or specify the failure output you are looking for (if you want to
ignore some other episodic failures).

Do you find it useful?
I use it for several years for all kinds of episodic failures (not just Go btw).

Change-Id: I06553345b76768a819412acb45f9bdfb3bababf7
Reviewed-on: https://go-review.googlesource.com/9373
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

sshetty10/tools,glasser/golang-tools,sshetty10/tools,argandas/tools,syreclabs/go-tools,magiccao/tools,josharian/tools,springning/tools,glasser/golang-tools,syreclabs/go-tools,cw2018/tools,cmars/tools,sshetty10/tools,cw2018/tools,cw2018/tools,runcom/tools,argandas/tools,cmars/tools,jdhenke/tools,runcom/tools,golang/tools,golang/tools,syreclabs/go-tools,matryer/tools,jdhenke/tools,cmars/tools,josharian/tools,cw2018/tools,jdhenke/tools,syreclabs/go-tools,golang/tools,matryer/tools,runcom/tools,argandas/tools,nicot/tools,josharian/tools,runcom/tools,syreclabs/go-tools,glasser/golang-tools,springning/tools,nicot/tools,nicot/tools,magiccao/tools,sshetty10/tools,syreclabs/go-tools,argandas/tools,golang/tools,golang/tools,springning/tools,josharian/tools,matryer/tools,cmars/tools,glasser/golang-tools,nicot/tools,matryer/tools,springning/tools,magiccao/tools,jdhenke/tools,magiccao/tools