Modified “log.slow-query-file” do not take effect when using tiup

[wxiaoke]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

1. Modify the following parameter using tiup cluster edit-config tidb-test1
       log.slow-query-file: 1111.log
2. Reload tidb to make the parameter affect 

2. What did you expect to see?
   Configuration takes effect

3. What did you see instead?
   The file (conf/tidb.toml) takes effect, but the location of slow log does not change as expected.
   Observe that the script (run_tidb.sh) specifies the location of the slow log file

4. What version of TiUP are you using (tiup --version)?
   1.5.1, 1.4.3; I think that this problem has nothing to do with the tiup version