Fixed func_time.test that was depending on current time

mysql-test/main/func_time.result

@@ -3567,6 +3567,7 @@ DROP TABLE t1;
 #
 # MDEV-15363 Wrong result for CAST(LAST_DAY(TIME'00:00:00') AS TIME)
 #
+set timestamp=unix_timestamp('2018-08-02 10:10:10');
 SELECT
 LAST_DAY(TIME'00:00:00') AS c1,
 CAST(CAST(LAST_DAY(TIME'00:00:00') AS DATE) AS TIME) AS c2,

mysql-test/main/func_time.test

@@ -2159,6 +2159,7 @@ DROP TABLE t1;
 --echo # MDEV-15363 Wrong result for CAST(LAST_DAY(TIME'00:00:00') AS TIME)
 --echo #
 
+set timestamp=unix_timestamp('2018-08-02 10:10:10');
 SELECT
   LAST_DAY(TIME'00:00:00') AS c1,
   CAST(CAST(LAST_DAY(TIME'00:00:00') AS DATE) AS TIME) AS c2,