Fix the restore data example

Fixes: #18872

For backup, restore case, we usually restore in same directory, so
when we untar it, we not need go to /dbdata directory, wich could
result in /dbdata/dbdata, this fix make it untar directly. The directory
/dbdata would be same as old container /dbdata.

Signed-off-by: Kai Qiang Wu(Kennan) <wkqwu@cn.ibm.com>