Switch to standard SI prefixes for kilobyte etc

Previously, powers of 1024 were used in formatting human-readable
strings for file sizes, in contrast with international and industry
standards. With this change, we switch to powers of 1000, as
standardized in SI and others.

Bug: 27672362
Change-Id: I34ae16bb68a28e60b09a7c17ac3b1d5ab9ddbeea