autotest: Set servo state as SERVO_SERIAL_MISMATCH

Cherry picked from labpack change http://crrev.com/c/2849388

Additional extend logic to verify is root servo present

BUG=b:184868548
TEST=run local repair

Change-Id: I095b8f7f61582cbe836656aa89b3672594eca3e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/labpack/+/2849388
Tested-by: Otabek Kasimov <otabek@google.com>
Commit-Queue: Otabek Kasimov <otabek@google.com>
Reviewed-by: Garry Wang <xianuowang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2864658
Auto-Submit: Otabek Kasimov <otabek@google.com>
diff --git a/server/hosts/servo_constants.py b/server/hosts/servo_constants.py
index d662014..09e3436 100644
--- a/server/hosts/servo_constants.py
+++ b/server/hosts/servo_constants.py
@@ -54,6 +54,7 @@
 SERVO_STATE_NO_SSH = 'NO_SSH'
 SERVO_STATE_SERVO_HOST_ISSUE = 'SERVO_HOST_ISSUE'
 SERVO_STATE_NOT_CONNECTED = 'NOT_CONNECTED'
+SERVO_STATE_SERIAL_MISMATCH = 'SERVO_SERIAL_MISMATCH'
 SERVO_STATE_NEED_REPLACEMENT = 'NEED_REPLACEMENT'
 SERVO_STATE_CR50_CONSOLE_MISSING = 'CR50_CONSOLE_MISSING'
 SERVO_STATE_CCD_TESTLAB_ISSUE = 'CCD_TESTLAB_ISSUE'