vm_tools: Start vm_concierge on "starting arcvm-pre-login-services"

This change modifies vm_concierge.conf to start Concierge with
arcvm-pre-login-services, which is started by Chrome at the login
screen. This allows mini-ARCVM to be started at the login screen.

BUG=b:144542975
TEST=tast run <DUT> arc.Boot.vm crostini.Basic.stretch_amd64_stable

Change-Id: Id8b57cb7567daa44703b51c0b5311faa0f8d7b7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2573417
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
Tested-by: Willie Koomson <wvk@google.com>
Commit-Queue: Willie Koomson <wvk@google.com>
diff --git a/vm_tools/init/vm_concierge.conf b/vm_tools/init/vm_concierge.conf
index 9719a4d..ef2390f 100644
--- a/vm_tools/init/vm_concierge.conf
+++ b/vm_tools/init/vm_concierge.conf
@@ -8,7 +8,7 @@
 # Start the VM concierge service, which is responsible for managing all the
 # VMs running in the system.
 
-start on start-user-session
+start on start-user-session or starting arcvm-pre-login-services
 stop on stopping ui
 respawn
 expect fork