respect the origin name of table

[july2993]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.
   load a table with an upper case table name.

2. What did you expect to see?
   the table create by lightning should have the same name.

3. What did you see instead?
   the table name is changed to the lower case name

4. Versions of the cluster

   • TiDB-Lightning version (run tidb-lightning -V):
     3.0.12

     (paste TiDB-Lightning version here)
     

   • TiKV-Importer version (run tikv-importer -V)

     (paste TiKV-Importer version here)
     

   • TiKV version (run tikv-server -V):

     (paste TiKV version here)
     

   • TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

     (paste TiDB cluster version here)
     

   • Other interesting information (system version, hardware config, etc):

5. Screenshot/exported-PDF of Grafana dashboard or metrics' graph in Prometheus for TiDB-Lightning if possible
   

[july2993]

should be fix by #319 and pingcap/tidb-tools#342
cc @lichunzhu