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 <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Xixuan Wu <xixuan@chromium.org>
diff --git a/xbuddy.py b/xbuddy.py
index 26ea11f..d0bd8e3 100644
--- a/xbuddy.py
+++ b/xbuddy.py
@@ -47,6 +47,7 @@
 RECOVERY = 'recovery'
 STATEFUL = 'stateful'
 AUTOTEST = 'autotest'
+FACTORY_SHIM = 'factory_shim'
 
 # Local build constants
 ANY = "ANY"
@@ -66,6 +67,7 @@
     DEV,
     BASE,
     RECOVERY,
+    FACTORY_SHIM,
     FULL,
     STATEFUL,
     ANY,
@@ -76,6 +78,7 @@
     devserver_constants.IMAGE_FILE,
     devserver_constants.BASE_IMAGE_FILE,
     devserver_constants.RECOVERY_IMAGE_FILE,
+    devserver_constants.FACTORY_SHIM_IMAGE_FILE,
     devserver_constants.UPDATE_FILE,
     devserver_constants.STATEFUL_FILE,
     None, # For ANY.
@@ -88,6 +91,7 @@
     TEST,
     BASE,
     RECOVERY,
+    FACTORY_SHIM,
     FULL,
     STATEFUL,
     AUTOTEST,
@@ -97,6 +101,7 @@
     devserver_constants.TEST_IMAGE_FILE,
     devserver_constants.BASE_IMAGE_FILE,
     devserver_constants.RECOVERY_IMAGE_FILE,
+    devserver_constants.FACTORY_SHIM_IMAGE_FILE,
     devserver_constants.UPDATE_FILE,
     devserver_constants.STATEFUL_FILE,
     devserver_constants.AUTOTEST_DIR,
@@ -106,6 +111,7 @@
     artifact_info.TEST_IMAGE,
     artifact_info.BASE_IMAGE,
     artifact_info.RECOVERY_IMAGE,
+    artifact_info.FACTORY_SHIM_IMAGE,
     artifact_info.FULL_PAYLOAD,
     artifact_info.STATEFUL_PAYLOAD,
     artifact_info.AUTOTEST,