Implement setRoutingData for MetadataStoreDirectoryService

[NealSun96]

Issues

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

Fixes #841, #842, #843

Description

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

This PR implements setRoutingData, which was an endpoint that was defined but not finished. It allows users to overwrite whatever routing data there is for a namespace and replace it with a new set of data. This endpoint was designed with convenience in mind because it allows users to specify the routing data in one call instead of making multiple calls to create zkrealms and add sharding keys. This endpoint was originally designed to validate the input but now it doesn't, please refer #842 for the reasoning.

Related to this PR, we also discovered that there are problems related to the construction of TrieRoutingData in MetadataStoreDirectory. Please see #841 .

Lastly, we are also fixing the race conditions of writing operations in MetadataStoreDirectory which are discovered during the development. Please see #843.

Tests

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

[INFO] Tests run: 140, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 24.602 s - in TestSuite
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 140, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 53.115 s
[INFO] Finished at: 2020-03-02T14:38:49-08:00
[INFO] ------------------------------------------------------------------------

Commits

• My commits all reference appropriate Apache Helix GitHub issues in their subject lines, and I have squashed multiple commits if they address the same issue. 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

[narendly]

Nice work! 👍

[NealSun96]

This PR is ready to be merged, approved by @narendly
Final commit message:

Implement setRoutingData for MetadataStoreDirectoryService

Implement setRoutingData endpoint. Modify TrieRoutingData construction in MetadataStoreDirectory. Fix race conditions among writing operations in MetadataStoreDirectory.