build_sdk_board: add some logging of major commands

Log each emerge command we run since each one takes quite a long
time to complete to help with debugging/progress.

BUG=chromium:985180
TEST=`./build_sdk_board --board amd64-host` passes

Change-Id: Ife3f8a06a53d76f02142cff66cfa1cfcaa588cb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2212155
Reviewed-by: Alex Klein <saklein@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
1 file changed