Fix VACUUM_TRUNCATE_LOCK_WAIT_INTERVAL

lazy_truncate_heap() was waiting for
VACUUM_TRUNCATE_LOCK_WAIT_INTERVAL, but in microseconds
not milliseconds as originally intended.

Found by code inspection.

Simon Riggs

src/backend/commands/vacuumlazy.c

@@ -1747,7 +1747,7 @@ lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats)
 				return;
 			}
 
-			pg_usleep(VACUUM_TRUNCATE_LOCK_WAIT_INTERVAL);
+			pg_usleep(VACUUM_TRUNCATE_LOCK_WAIT_INTERVAL * 1000L);
 		}
 
 		/*