Use power_short_press() to power-on a DUT.

Same like a previous change: http://gerrit.chromium.org/gerrit/14049

The original power_normal_press delays 1.2 seconds. A fast machine boots to the
firmware screen in 1.2 seconds and it checks that the power button is pressed.
As a result, the machine is then shutdown. So we now change to use
power_short_press which is 0.1 second.

BUG=chromium-os:24754
TEST=run_remote_tests.sh --remote=$REMOTE_IP -a "xml_config=$OVERLAY_XML \
        servo_vid=0x18d1 servo_pid=0x5001" platform_InstallRecoveryImage

Change-Id: I6532d9134cdd7202a35e7f6f5886cb3e3a2a82ce
Reviewed-on: https://gerrit.chromium.org/gerrit/14237
Reviewed-by: Todd Broch <tbroch@chromium.org>
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
diff --git a/server/cros/servo.py b/server/cros/servo.py
index 42ab51e..707e974 100644
--- a/server/cros/servo.py
+++ b/server/cros/servo.py
@@ -235,7 +235,7 @@
 
     def boot_devmode(self):
         """Boot a dev-mode device that is powered off."""
-        self.power_normal_press()
+        self.power_short_press()
         self.pass_devmode()
 
 
@@ -369,7 +369,7 @@
         # Boot in recovery mode.
         try:
             self.enable_recovery_mode()
-            self.power_normal_press()
+            self.power_short_press()
             time.sleep(Servo.RECOVERY_BOOT_DELAY)
             self.set('usb_mux_sel1', 'dut_sees_usbkey')
             self.disable_recovery_mode()