hdctools: servo: Properly import HwDriverError

When catching exception from drivers, we want to be able to catch
HwDriverError. However, since HwDriverError is not properly imported to
current namespace, we actually generate an AttributeError when trying to
catch the original exception. This CL imports HwDriverError so that this
doesn't happen.

TEST=Generate an 'ecError' in EC driver and see the correct error
message using dut-control.

Signed-off-by: Vic Yang <victoryang@chromium.org>
Change-Id: I9cfeb0c42b92f86b6ab8c967f1593d3373b3991e
Reviewed-on: https://gerrit.chromium.org/gerrit/26223
Reviewed-by: Doug Anderson <dianders@chromium.org>
11 files changed