Lack of progress updates when migrating volumes

##### ISSUE TYPE
* Improvement Request

##### COMPONENT NAME

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Volume operations
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##### CLOUDSTACK VERSION

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4.19.1.1
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##### CONFIGURATION

##### OS / ENVIRONMENT
Ubuntu KVM

##### SUMMARY

When migrating volumes between storages the qemu-img command does not report any progress anywhere, when moving large volumes it's useful to know how it is going.
It would be beneficial to add "-p" "convert" switch to qemu-img to get a progress then send the stdout/stderr to the agent.log or syslog.

##### STEPS TO REPRODUCE
Migrate a large volume between different various storages.
Takes a long time with no way to check (unless you start inspecting target volumes that is).

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##### EXPECTED RESULTS

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Command returns some progress to the user/operator, either in UI , logs, both etc.
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##### ACTUAL RESULTS

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No progress reports of any sort.
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首先定位为 Ubuntu KVM 调用 qemu-img 的卷迁移路径，然后跟踪 agent.log 或 syslog 的输出在哪里处理。该 issue 提议显示 qemu-img convert 的进度，并期望操作人员能够在日志、UI 或两者中看到它；在大型卷迁移期间确认所选的输出位置。

由索引模型根据 Issue 内容生成。