skip the error log in TestAllocatePortInUse
skip the error log in TestAllocatePortInUse

We know we're going to see an error, so don't log it too:

	$ go test -run TestAllocatePortInUse
	2019/02/21 17:11:34 ERROR: pool could not allocate runner ...
	PASS
	ok      github.com/chromedp/chromedp    0.004s

chromedp/chromedp,knq/chromedp,chromedp/chromedp,knq/chromedp,knq/chromedp,chromedp/chromedp