Make ConnPoll stress test time based

Test now runs for fixed amount of time instead of a fixed number of iterations.
This should enable TravisCI to finish the test.

stress_test.go

@@ -44,9 +44,11 @@ func TestStressConnPool(t *testing.T) {
 		{"reset", func(p *pgx.ConnPool, n int) error { p.Reset(); return nil }},
 	}
 
-	actionCount := 5000
+	var timer *time.Timer
 	if testing.Short() {
-		actionCount /= 10
+		timer = time.NewTimer(5 * time.Second)
+	} else {
+		timer = time.NewTimer(60 * time.Second)
 	}
 	workerCount := 16
 
@@ -70,8 +72,11 @@ func TestStressConnPool(t *testing.T) {
 		go work()
 	}
 
-	for i := 0; i < actionCount; i++ {
+	var stop bool
+	for i := 0; !stop; i++ {
 		select {
+		case <-timer.C:
+			stop = true
 		case workChan <- i:
 		case err := <-errChan:
 			close(workChan)