[Fix] Fix bug in non-distributed multi-gpu training/testing

[ly015]

Motivation

Refer to open-mmlab/mmdetection#7019

For training, we use single gpu in non-distributed env like in mmdet#7019. For testing, we add --gpu-id argument to allow specifying the device, instead of using gpu-0 by force.

Modification

BC-breaking (Optional)

Use cases (Optional)

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
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• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

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2 out of 3 committers have signed the CLA.

✅ jin-s13
✅ ly015
❌ Canwang-sjtu
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Codecov Report

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