find left most node error (#142)
find left most node error (#142)

* CreateTableStmt and AlterTableStmt cluster name is null

Change-Id: Id5869961694fa11808db66ecf121d7cef0898f95

Signed-off-by: chenhao16 <22f4e5f4451ae2582742261da803947deef590f8@baidu.com>

* add des cluster when perform 'allter system add backend'

* find left most node error

cyongli/palo,morningman/palo,morningman/palo,imay/palo,imay/palo,imay/palo,morningman/palo,imay/palo,lingbin/palo,morningman/palo,imay/palo,morningman/palo,lingbin/palo,lingbin/palo,imay/palo,lingbin/palo,morningman/palo,cyongli/palo,lingbin/palo,cyongli/palo,cyongli/palo,cyongli/palo,lingbin/palo,cyongli/palo