autotest: Create servo_type in servo constants

Change-Id: I3fdb6c22c002198a8b6955877fc8828a4ed25d79
BUG=chromium:1059437
TEST=unitests
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2146070
Tested-by: Otabek Kasimov <otabek@google.com>
Reviewed-by: Garry Wang <xianuowang@chromium.org>
Commit-Queue: Otabek Kasimov <otabek@google.com>
diff --git a/server/hosts/servo_constants.py b/server/hosts/servo_constants.py
index 870733c..66d9bc9 100644
--- a/server/hosts/servo_constants.py
+++ b/server/hosts/servo_constants.py
@@ -38,6 +38,7 @@
 ENABLE_SSH_TUNNEL_FOR_SERVO = _CONFIG.get_config_value(
         'CROS', 'enable_ssh_tunnel_for_servo', type=bool, default=False)
 
+SERVO_TYPE_LABEL_PREFIX = 'servo_type'
 SERVO_STATE_LABEL_PREFIX = 'servo_state'
 SERVO_STATE_WORKING = 'WORKING'
 SERVO_STATE_BROKEN = 'BROKEN'