FAFT: Reboot DUT after prioritize the kernel A/B

After prioritize ther kernel A/B, should reboot the DUT to make it
effective.

BUG=None
TEST=Made the kernel B boot and ran firmware_UpdateKernelVersion test.

Change-Id: I65b8e32fabfe6965e77b830d6ce792cb18da3a6d
Reviewed-on: https://chromium-review.googlesource.com/302452
Commit-Ready: Wai-Hong Tam <waihong@chromium.org>
Tested-by: Wai-Hong Tam <waihong@chromium.org>
Reviewed-by: Shelley Chen <shchen@chromium.org>
diff --git a/server/cros/faft/firmware_test.py b/server/cros/faft/firmware_test.py
index 922649c..6cc7f04 100644
--- a/server/cros/faft/firmware_test.py
+++ b/server/cros/faft/firmware_test.py
@@ -554,6 +554,7 @@
                         from_part=self.OTHER_KERNEL_MAP[part],
                         to_part=part)
             self.reset_and_prioritize_kernel(part)
+            self.switcher.mode_aware_reboot()
 
     def set_hardware_write_protect(self, enable):
         """Set hardware write protect pin.