xbuddy: add a factory_shim alias

This allows you to do:
  cros flash usb:// xbuddy://remote/samus/latest-canary/factory_shim

BUG=None
TEST=ran above flash command and it downloaded & flashed factory_install_shim.bin

Change-Id: Icf0f0e016c344be1b4e34f901da68c64dcef2492
Reviewed-on: https://chromium-review.googlesource.com/380355
Commit-Ready: Mike Frysinger <[email protected]>
Tested-by: Mike Frysinger <[email protected]>
Reviewed-by: Xixuan Wu <[email protected]>
diff --git a/devserver_constants.py b/devserver_constants.py
index 84ef53a..9a72087 100644
--- a/devserver_constants.py
+++ b/devserver_constants.py
@@ -27,6 +27,7 @@
 BASE_IMAGE_FILE = 'chromiumos_base_image.bin'
 IMAGE_FILE = 'chromiumos_image.bin'
 FACTORY_IMAGE_FILE = 'factory_test/chromiumos_factory_image.bin'
+FACTORY_SHIM_IMAGE_FILE = 'factory_shim/factory_install_shim.bin'
 RECOVERY_IMAGE_FILE = 'recovery_image.bin'
 TEST_IMAGE_FILE = 'chromiumos_test_image.bin'