cros_run_bvt: fix the test name

This http://crrev.com/c/2333435 change the name to
platform_ServoPowerStateController.USBUnplugged. We need to correct
cros_run_bvt to avoid the error

BUG=b:165437573
TEST=no error popped out after executing `cros_run_bvt --labqual`

Change-Id: Ia71ce454ddefc1373b0862559213611ce693d603
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/2368792
Reviewed-by: Dhanya Ganesh <dhanyaganesh@chromium.org>
Reviewed-by: Ross Zwisler <zwisler@google.com>
Tested-by: Zhuohao Lee <zhuohao@chromium.org>
Commit-Queue: Zhuohao Lee <zhuohao@chromium.org>