Move wait_fw_screen_and_plug_usb() to FAFTSequence base class.

BUG=chromium-os:19710
TEST=run_remote_tests.sh --remote=$REMOTE_IP -a "xml_config=$OVERLAY_XML \
        servo_vid=0x18d1 servo_pid=0x5001" RecoveryButton/control.normal
     run_remote_tests.sh --remote=$REMOTE_IP -a "xml_config=$OVERLAY_XML \
        servo_vid=0x18d1 servo_pid=0x5001" DevTriggerRecovery/control

Change-Id: If54ad1e670f32cd57a9914e0f296f2fc633f97e2
Reviewed-on: https://gerrit.chromium.org/gerrit/12480
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Reviewed-by: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
diff --git a/server/cros/faftsequence.py b/server/cros/faftsequence.py
index 6bb4941..49b9485 100644
--- a/server/cros/faftsequence.py
+++ b/server/cros/faftsequence.py
@@ -284,6 +284,14 @@
         self.servo.ctrl_d()
 
 
+    def wait_fw_screen_and_plug_usb(self):
+        """Wait for firmware warning screen and then unplug and plug the USB."""
+        time.sleep(self.FIRMWARE_SCREEN_DELAY)
+        self.servo.set('usb_mux_sel1', 'servo_sees_usbkey')
+        time.sleep(self.USB_PLUG_DELAY)
+        self.servo.set('usb_mux_sel1', 'dut_sees_usbkey')
+
+
     def setup_tried_fwb(self, tried_fwb):
         """Setup for fw B tried state.