Backoff and Randomness additions for use in client utilities

Updated String to use int, and int not to panic, and panic to test panic
Format fixes.

pkg/util/backoff_test.go

@@ -46,6 +46,14 @@ func TestSlowBackoff(t *testing.T) {
 		}
 		b.Next(id, tc.Now())
 	}
+
+	//Now confirm that the Reset cancels backoff.
+	b.Next(id, tc.Now())
+	b.Reset(id)
+	if b.Get(id) != 0 {
+		t.Errorf("Reset didn't clear the backoff.")
+	}
+
 }
 
 func TestBackoffReset(t *testing.T) {