isolation for internal tables (e.g. meta) and uesr tables

一时手残把meta_table给disable掉了。。。
然后任何meta操作都不成功，想要enable起来meta_table首先要写meta_table，但是meta_table已经unload掉，没法写。。。死锁了。

重启master可以暂时解决这个问题。

No files, tests, or entry points are identified. Reproduce the reported sequence by disabling and unloading meta_table, then attempt a meta operation and re-enable operation; define isolation between internal and user tables as done only when this no longer deadlocks and the documented restart workaround is unnecessary.

Written by the indexing model from the issue text.