autotest: add a default host_scheduler_minimum_tick_sec to global_config

BUG=chromium:719778
TEST=None

Change-Id: I8facccde2bcfa530f209f1977745993e85e569e9
Reviewed-on: https://chromium-review.googlesource.com/499391
Reviewed-by: Allen Li <ayatane@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index a0668da..2d78591 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -199,6 +199,7 @@
 max_transfer_processes: 50
 tick_pause_sec: 5
 minimum_tick_sec: 0.5
+host_scheduler_minimum_tick_sec: 3
 clean_interval_minutes: 5
 drones: SET IN SHADOW CONFIG
 drone_installation_directory: /usr/local/autotest