autotest: servo: Produce more meaningful exception messages from servod.

The underlying exception in servod is masked currently by the
xmlrpclib.Fault exception.  This CL changes that relatively
meaningless message like:
 <Fault 1: "<type 'exceptions.AttributeError'>:'tca6416' object has no
 attribute 'hw_driver'">

To something more meaningful like:
  FAIL: Setting 'lid_open' to 'no' :: No control named lid_open

BUG=chrome-os-partner:10908
TEST=./run_remote_tests.sh --remote=<host> --servo platform_CloseOpenLid --board=<board>

Tested by modifying servod's xml files to remove lid_open control to
see failure.

Change-Id: I594dc13f8fff4c43e35f0e020da9473c11c7453c
Reviewed-on: https://gerrit.chromium.org/gerrit/27243
Tested-by: Todd Broch <tbroch@chromium.org>
Reviewed-by: Vic Yang <victoryang@chromium.org>
Commit-Ready: Todd Broch <tbroch@chromium.org>
1 file changed