Run scrape loop with interval 1 instead of 0

0 is considered an invalid interval by time.NewTicker() and will cause a
panic if control reaches that point. Given the vagaries of timekeeping,
this may occasionally happen and make this test unstable.

retrieval/scrape_test.go

@@ -329,7 +329,7 @@ func TestScrapeLoopStop(t *testing.T) {
 
 	runDone := make(chan struct{})
 	go func() {
-		sl.run(0, 0, nil)
+		sl.run(1, 0, nil)
 		close(runDone)
 	}()