### Motivation

Fix #4732

### Modifications

Add options to rewrite the namespace delimiter, disable by default

Enable rewrite namespace delimiter can work well with superset:
<img width="1279" alt="superset" src="https://user-images.githubusercontent.com/12592133/61385412-f0f35700-a8e4-11e9-87b2-a31b62128b58.png">

### Does this pull request potentially affect one of the following parts:

*If `yes` was chosen, please highlight the changes*

  - Dependencies (does it add or upgrade a dependency): (no)
  - The public API: (no)
  - The schema: (no)
  - The default values of configurations: (no)
  - The wire protocol: (no)
  - The rest endpoints: (no)
  - The admin cli options: (no)
  - Anything that affects deployment: (no)

### Documentation

  - Does this pull request introduce a new feature? (no)

(cherry picked from commit 6ddd51ff)