runtime/pprof: fix flaky TestCPUProfileMultithreaded test

It's too sensitive.

Fixes bug 7095

R=golang-codereviews, iant, minux.ma, rsc
CC=golang-codereviews
https://golang.org/cl/50470043

src/pkg/runtime/pprof/pprof_test.go

@@ -142,7 +142,11 @@ func testCPUProfile(t *testing.T, need []string, f func()) {
 		t.Logf("no CPU profile samples collected")
 		ok = false
 	}
-	min := total / uintptr(len(have)) / 3
+	// We'd like to check a reasonable minimum, like
+	// total / len(have) / smallconstant, but this test is
+	// pretty flaky (see bug 7095).  So we'll just test to
+	// make sure we got at least one sample.
+	min := uintptr(1)
 	for i, name := range need {
 		if have[i] < min {
 			t.Logf("%s has %d samples out of %d, want at least %d, ideally %d", name, have[i], total, min, total/uintptr(len(have)))