fix data space reporting from Kb/Mb to KiB/MiB

 Fix data space reporting from Kb/Mb to KiB/MiB.  Currently "docker info" reports data/metadata space using "Kb/Mb" instead of the expected "KB/MB". "Mb" actually means megabits, but actually this should be MiB and so on.   Mentioned in issue #7429 .