Normalize DiskIOMeter bar by number of disks #4622

Job	Run time
build-freebsd-latest-clang	2m 4s
build-dragonflybsd-latest-gcc	2m 16s
build-netbsd-latest-gcc	3m 8s
build-macos-latest-clang	40s
build-openbsd-latest-clang	2m 13s
build-solaris-latest-gcc	3m 21s
build-ubuntu-latest-clang-analyzer	1m 4s
build-ubuntu-latest-clang-sanitizer	1m 4s
build-ubuntu-latest-full-featured-clang	1m 3s
build-ubuntu-latest-full-featured-gcc	51s
build-ubuntu-latest-gcc-static	53s
build-ubuntu-latest-minimal-clang	1m 2s
build-ubuntu-latest-minimal-gcc	39s
build-ubuntu-latest-pcp	27s
lint-pcp-config	4s
lint-whitespace	4s
	20m 53s

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