expand the BDB acronym in a few key places

For people not readily familiar with the BDB acronym, expand it in
a few README files and usage strings.

TEST=looked at help output

Change-Id: I2523e1a289815dd0eaea093c086bc75093579808
Reviewed-on: https://chromium-review.googlesource.com/414244
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
5 files changed