Fix BestPossibleVerifier attempting to verify all WAGED resources

[MarkGaox]

Issues

• My PR addresses the following Helix issues and references them in the PR description:
  BestPossibleExternalViewVerifier Verifies All Resources Instead of Specified Resource Only #2954

Description

• Here are some details about my PR, including screenshots of any UI changes:
  This PR fixes the issue by retaining only the requested resource before verify the external view.

Tests

• The following tests are written for this issue:
  mvn test -Dtest=TestClusterVerifier -pl helix-core

Changes that Break Backward Compatibility (Optional)

• My PR contains changes that break backward compatibility or previous assumptions for certain methods or API. They include:

(Consider including all behavior changes for public methods or API. Also include these changes in merge description so that other developers are aware of these changes. This allows them to make relevant code changes in feature branches accounting for the new method/API behavior.)

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)

[MarkGaox]

Approved by @zpinto, TFTR. Final commit message: "Fix BestPossibleVerifier attempting to verify all WAGED resources"