FAFT: Use better naming for FAFTConfig and get_usbdisk_path_on_dut

The Config imported from faft config is renamed to FAFTConfig.
And the method get_dut_usb_dev is renamed to get_usbdisk_path_on_dut.

BUG=None
TEST=Manual
Ran firmware_SelfSignedBoot test on Spring and passed.

Change-Id: Icb528bec584a8fa813d98e5fe661913a44f90391
Reviewed-on: https://chromium-review.googlesource.com/67047
Reviewed-by: Yusuf Mohsinally <mohsinally@chromium.org>
Commit-Queue: Wai-Hong Tam <waihong@chromium.org>
Tested-by: Wai-Hong Tam <waihong@chromium.org>
4 files changed