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 .

Signed-off-by: Vivek Dasgupta <vdasgupt@redhat.com>