FIXED exiting queue thread and wait remain finish & auto create cgrou…

[yungoo]

What changes were proposed in this pull request?

Why are the changes needed?

When i login user in tenant, the ObClient is hanging at Welcome to oceanbase..., it's because the ObTenant will not create the ngroup ctrl files when ObTenant::init. so change ObCgroupCtrl::write_string_to_file_ to allow auto create cgroup control file.

使用root登录租户时一直卡在Welcome to Oceanbase XXX，发现MySQL请求全部堆积未处理。租户的请求按设计应从ResourceGroup的请求队列出队，而请求实际入队的却是ObTenant的队列(参照：ObTenant::recv_request/ObTenant::get_new_request)。由于cgroup下租户的配置文件不会自动创建(查看：ObCgroupCtrl::write_string_to_file_），导致Tenant未正确初始化group_map_（参照：ObTenant::init），从而消息放入错误的队列，永远不会被消费。

Will break the compatibility? How if so?

NO

Does this PR introduce any user-facing change?

no need to manually create cgroup control files.

How was this patch tested?

login root@tenant after tenant created without manualy create cgroup files, the MySQL client should work.

Checklist

• [Y] I've run the tests to see all new and existing tests pass.
• [N] If this Pull Request resolves an issue, I linked to the issue in the text above.
• [N] I've informed the technical writer about the documentation change if necessary.

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