<fix>[compute]: respect vm.migrationQuantity during host maintenance

[zstack-robot-1]

Root Cause

In HostBase.maintenanceHook(), when any OrderVmBeforeMigrationDuringHostMaintenanceExtensionPoint returns an ordered VM list, migrateQuantity was unconditionally forced to 1 (line 416). Since HaManagerImpl always returns non-null (even when no VMs have HA tags), the user-configured vm.migrationQuantity global config was never effective during host maintenance mode.

Solution

Remove the migrateQuantity = 1 override. The VM ordering is preserved by list position — HA VMs remain at the front of the list. The While loop processes items in order with the user-configured concurrency level, so HA VMs are still prioritized in early batches.

Testing

• Compile verified: mvn compile -pl compute -am -Dmaven.test.skip
• Logic review: While.step(callback, migrateQuantity) processes N items concurrently from the ordered list, preserving priority ordering

Jira

Resolves: ZSTAC-81354

Note: Companion MR in premium repo (HaManagerImpl returns null when no HA tags exist).

sync from gitlab !9209

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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走览

移除了在扩展点提供VM顺序时强制将migrateQuantity设置为1的赋值逻辑。代码现在保留现有的migrateQuantity值，仅记录有序的VM列表和当前迁移数量，而非强制单个迁移量。

变更

内聚组 / 文件(s)	摘要
VM迁移数量逻辑 compute/src/main/java/org/zstack/compute/host/HostBase.java	移除强制migrateQuantity = 1的赋值，改为保留现有数量值并记录有序VM列表。

代码审查工作量

🎯 1 (Trivial) | ⏱️ ~3 分钟

诗

🐰 一份改动小而精，
移除强制是本义，
迁移量得保本真，
顺序记录显风云，
代码简洁更通透！

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	标题清晰总结了主要变更内容，遵循规定的格式 [scope]: ，长度68字符（≤72），完全相关且描述性强。
Description check	✅ Passed	描述详细阐述了根本原因、解决方案、测试验证和相关 Jira 号，与代码变更直接相关且信息充分。

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✨ Finishing Touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch sync/ye.zou/fix/ZSTAC-81354

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