[autotest] Add an option in provision_FirmwareUpdate to stage CrOS image on USB

BUG=chromium:517551
TEST=set stage_image_to_usb to True and run a suite
./site_utils/run_suite.py -b veyron_jerry  -i
veyron_jerry-release/R51-8099.0.0  -s dummy --firmware_rw_build
veyron_jerry-firmware/R41-6588.182.0

Change-Id: Ibd3284154b72decde1faa54f2ee3b360c8024109
Reviewed-on: https://chromium-review.googlesource.com/337347
Commit-Ready: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@google.com>
Reviewed-by: Wai-Hong Tam <waihong@chromium.org>
diff --git a/server/cros/servo/servo.py b/server/cros/servo/servo.py
index 6118f66..e3a0acd 100644
--- a/server/cros/servo/servo.py
+++ b/server/cros/servo/servo.py
@@ -612,19 +612,17 @@
 
     def install_recovery_image(self, image_path=None,
                                make_image_noninteractive=False):
-        """Install the recovery image specied by the path onto the DUT.
+        """Install the recovery image specified by the path onto the DUT.
 
         This method uses google recovery mode to install a recovery image
         onto a DUT through the use of a USB stick that is mounted on a servo
         board specified by the usb_dev.  If no image path is specified
         we use the recovery image already on the usb image.
 
-        @param image_path Path on the host to the recovery image.
-        @param make_image_noninteractive Make the recovery image
-                                         noninteractive, therefore
-                                         the DUT will reboot
-                                         automatically after
-                                         installation.
+        @param image_path: Path on the host to the recovery image.
+        @param make_image_noninteractive: Make the recovery image
+                noninteractive, therefore the DUT will reboot automatically
+                after installation.
         """
         self.image_to_servo_usb(image_path, make_image_noninteractive)
         self._power_state.power_on(rec_mode=self._power_state.REC_ON)