Add an internal storage barrier to postgresql

[hzy46]

to fix #5341

[coveralls]

Coverage remained the same at 34.07% when pulling 900380c on zhiyuhe/fix_master_db_bug into d9b3d7d on master.

[Binyang2014]

Why not move internal storage into postgresql folder. If it only used by postgresql

[hzy46]

Why not move internal storage into postgresql folder. If it only used by postgresql

For current usage, there's no difference between putting it in postgresql and internal-storage.

But if there are other services relying on internal-storage, putting this in internal-storage can make it easier to reuse. It may happen in the future.

[Binyang2014]

It's ok for me as a hot-fix. Please create another issue to move to to postgresql. Then we can make the code much more clean and leverage the k8s mechanism.

[hzy46]

It's ok for me as a hot-fix. Please create another issue to move to to postgresql. Then we can make the code much more clean and leverage the k8s mechanism.

I have record the new design to #5344 . It does have some advantages. However, considering there's only one service using internal storage now, it may be not worth the effort to implement the new mechanism. We can leave it to a future work.