Support specifying a given shellball when running firmware update FAFTs

Provide an argument "shellball" in the firmware update FAFTs. If the arguemnt
is left blank, it used /usr/sbin/chromeos-firmwareupdate as shellball.

This version only modifies one test case.

BUG=chrome-os-partner:14361
TEST=run_remote_tests.sh -a "shellball=[given_shellball]" [test]

Change-Id: If517bd69dade0ce00fecc1e1e87fed56076449c4
Reviewed-on: https://gerrit.chromium.org/gerrit/34266
Reviewed-by: Tom Wai-Hong Tam <waihong@chromium.org>
Commit-Ready: Chun-Ting Chang <ctchang@chromium.org>
Tested-by: Chun-Ting Chang <ctchang@chromium.org>
7 files changed