[7.15](backport #28456) Fix rds metricset cpu.total.pct

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This is an automatic backport of pull request #28456 done by Mergify.

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• Start Time: 2021-10-18T21:31:37.244+0000

• Duration: 90 min 11 sec

• Commit: 9a63a85

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Test	Results
Failed	0
Passed	2654
Skipped	232
Total	2886

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