[autotest] Add switch to enable/disable devserver and drone election in restricted subnet.

This allows devserver and drone election in restricted subnet to be enabled/
disabled separatedly.

BUG=chromium:574872
TEST=unittest

Change-Id: If2c3d1ad1bd9be5546bf2f8a027bcd88627ae2c5
Reviewed-on: https://chromium-review.googlesource.com/322468
Commit-Ready: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@google.com>
Reviewed-by: Dan Shi <dshi@google.com>
diff --git a/global_config.ini b/global_config.ini
index fc83413..1b324ad 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -315,6 +315,10 @@
 # A list of restricted subnets, in the format of ip:mask_bits, e.g., 10.0.0.1:24
 restricted_subnets:
 
+# Flags to enable/disable devserver and drone election in resctricted subnet.
+enable_drone_in_restricted_subnet: False
+enable_devserver_in_restricted_subnet: False
+
 # Set to True for test to prefer devserver in the same subnet.
 prefer_local_devserver: False