Normalize DiskIOMeter bar by number of disks #4620

Job	Run time
build-macos-latest-clang	48s
build-freebsd-latest-clang	2m 16s
build-dragonflybsd-latest-gcc	2m 34s
build-openbsd-latest-clang	2m 36s
build-solaris-latest-gcc	4m 7s
build-netbsd-latest-gcc	2m 55s
build-ubuntu-latest-clang-analyzer	1m 13s
build-ubuntu-latest-clang-sanitizer	58s
build-ubuntu-latest-full-featured-clang	1m 4s
build-ubuntu-latest-full-featured-gcc	49s
build-ubuntu-latest-gcc-static	52s
build-ubuntu-latest-minimal-clang	57s
build-ubuntu-latest-minimal-gcc	40s
build-ubuntu-latest-pcp	26s
lint-pcp-config	3s
lint-whitespace	2s
	22m 20s

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