Make ZkCacheBaseDataAccessor and ZkHelixPropertyStore realm-aware

[narendly]

Issues

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

Resolves #862

Description

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

This commit makes both ZkCacheBaseDataAccessor and ZkHelixPropertyStore realm-aware by choosing the appropriate realm-aware ZkClients in the constructor. Also, we add a Builder here to give users options to set Connection config and Client config.
Note that ZkHelixPropertyStore extends CacheBaseDataAccessor so there is no change needed.

Tests

• The following tests are written for this issue:

The following tests cover ZkCacheBaseDataAccessor:

TestZkCacheAsyncOpSingleThread,TestZkCacheSyncOpSingleThread,TestWtCacheSyncOpSingleThread,TestWtCacheAsyncOpMultiThread

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

mvn test -Dtest=TestZkCacheAsyncOpSingleThread,TestZkCacheSyncOpSingleThread,TestWtCacheSyncOpSingleThread,TestWtCacheAsyncOpMultiThread

[INFO] Tests run: 6, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 21.875 s - in TestSuite
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 6, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 49.191 s
[INFO] Finished at: 2020-03-04T20:33:05-08:00
[INFO] ------------------------------------------------------------------------

helix-core:

[INFO] Results:
[INFO] 
[ERROR] Failures: 
[ERROR]   TestEnableCompression.testEnableCompressionResource:108 expected:<true> but was:<false>
[ERROR]   TestControllerLeadershipChange.testMissingTopStateDurationMonitoring:262 expected:<true> but was:<false>
[INFO] 
[ERROR] Tests run: 1083, Failures: 2, Errors: 0, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  01:09 h
[INFO] Finished at: 2020-03-04T21:54:11-08:00
[INFO] ------------------------------------------------------------------------

mvn test -Dtest=TestEnableCompression,TestControllerLeadershipChange

[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 33.611 s - in TestSuite
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  01:15 min
[INFO] Finished at: 2020-03-04T21:56:37-08:00
[INFO] ------------------------------------------------------------------------

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)

[junkaixue]

LGTM. But please address remaining concerns.

[narendly]

This PR is ready to be merged, approved by @dasahcc

This commit makes both ZkCacheBaseDataAccessor and ZkHelixPropertyStore realm-aware by choosing the appropriate realm-aware ZkClients in the constructor. Also, we add a Builder here to give users options to set Connection config and Client config.
Note that ZkHelixPropertyStore extends CacheBaseDataAccessor so there is no change needed.