faft: Speed up by moving the GBB flag setup to FAFTSequence

We now check/change GBB flags only on the first test of the test suite.
Moving all the required GBB flag change in FAFTSequence can save time for
duplicate check/change.

BUG=chromium-os:34392
TEST=run_remote_tests.sh --board daisy --remote dut DevScreenTimeout \
     RollbackFirmware/control$

Change-Id: I8417e5e1c79a8e7b18fadf54ec75c736dfcdcafd
Reviewed-on: https://gerrit.chromium.org/gerrit/35940
Reviewed-by: Vic Yang <victoryang@chromium.org>
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
3 files changed