Fix routingDataSourceType not configured in helix rest

[huizhilu]

Issues

• My PR addresses the following Helix issues and references them in the PR description:

Fixes #1308

Description

• Here are some details about my PR, including screenshots of any UI changes:

Routing data source type is not set in helix rest when creating a realm-aware zkclient. This PR sets the source type to HTTP in helix rest.

Tests

• The following tests are written for this issue:

(List the names of added unit/integration tests)

• The following is the result of the "mvn test" command on the appropriate module:

(Before CI test pass, please copy & paste the result of "mvn test")

Documentation (Optional)

• In case of new functionality, my PR adds documentation in the following wiki page:

(Link the GitHub wiki you added)

Commits

• My commits all reference appropriate Apache Helix GitHub issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Code Quality

• My diff has been formatted using helix-style.xml
  (helix-style-intellij.xml if IntelliJ IDE is used)

[huizhilu]

Verified it works after this change.

{
  "MULTI_ZK_ENABLED" : "true",
  "IS_DEFAULT" : "false",
  "MSDS_ENDPOINT" : "http://<rest-server>/admin/v2/namespaces/test",
  "NAME" : "test"
}

curl localhost:8100/admin/v2/namespaces/test/clusters                
{
  "clusters" : [ "cluster-1", "cluster-2"]
}

The reason why we don’t catch the defect in helix rest tests is we don’t run tests against multiZk enabled. I think we should do so. We'll enable this in another PR.

This PR is ready to be merged.