[autotest] Specify which afe server to talk to for suite scheduler

Add a setting "suite_scheduler_afe" to [SERVER]
If set, suite scheduler will talk to this afe server.
otherwise, it will default to [SERVER]:hostname

TEST=Ran suite_scheduler with and without the setting in shadow config.
BUG=chromium:513062

Change-Id: I88e179a2d8306356e7e5316345f524b4a9982141
Reviewed-on: https://chromium-review.googlesource.com/291456
Reviewed-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Fang Deng <fdeng@chromium.org>
Tested-by: Fang Deng <fdeng@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index d0abb88..4e942bc 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -128,6 +128,10 @@
 # like scheduler, host-scheduler and suite-scheduler.
 use_server_db: False
 
+# Suite scheduler afe server
+# If no specified, will default to [SERVER]: hostname
+suite_scheduler_afe:
+
 [SCHEDULER]
 die_on_orphans: False
 enable_scheduler: True
@@ -321,4 +325,4 @@
 # User that runs the autoserv process in the host of the container.
 # The user is passed to a container through global config file so a process
 # running inside the container can use the same user to make RPC.
-user:
\ No newline at end of file
+user: