Fix SWAP_IN InstanceOperation to respect HELIX_ENABLED false

[zpinto]

Issues

• Fix SWAP to respect instance disabled state to send all assigned partitions to OFFLINE state. SWAP_IN instance will still have the same assignment as SWAP_OUT instance.
• Remove unnecessary logic to handle SWAP_IN node in preferenceList, this was from old approach.

Description

Previously, when a swap is initiated and the swap-in node has HELIX_ENABLED set to false, the replicas assigned to it are not sent to the OFFLINE state. In order to align with the behavior of HELIX_ENABLED = false, we will now send all assigned replicas to OFFLINE state. When the SWAP_IN instance is re-enabled, it will receive upward state transitions for its replicas.

Tests

• Add test testNodeSwapDisableAndReenable

Changes that Break Backward Compatibility (Optional)

Removed some public methods; however, they were not in an open source release and would likely cause more confusion if they were left.

Documentation (Optional)

NA

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
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  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]

LGTM!

[zpinto]

This PR is ready to be merged!

Final commit message:
In order to align with the behavior of HELIX_ENABLED = false, we will now send all assigned replicas to OFFLINE state. When the SWAP_IN instance is re-enabled, it will receive upward state transitions for its replicas.