bdb: Rename subkey to datakey

This patch replaces subkey with datakey to make name use consistent
with the design document.

BUG=chrome-os-partner:51908
BRANCH=tot
TEST=make runtests

Change-Id: I3690abd51e6c18c5a1094a8449f375d803c7e0b2
Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/342199
Reviewed-by: Randall Spangler <rspangler@chromium.org>
9 files changed