autotest: servo: allow host to connect to multiple servos in parallel

Servo debug board has an EEPROM that when probably programmed holds a
USB vendor id, USB product id and USB iSerial which can be used to
uniquely identify a servo.  This changelist allows one host to run
multiple servo-based autotests in parallel by referencing the specific
servo/servod via

  vid : USB vendor id
  pid : USB product id
  serialname : USB iSerial name
  port : unique socket port servod will be listening on

BUG=chrome-os-partner:4123
TEST=manual, run platform_CloseOpenLid from host with multiple servo's
connected.  One had servo's EEPROM programmed with a serialname so it
could be addressed.

Change-Id: I6369316d60f106d92b1b92665a6aaf26a22c6375
Reviewed-on: http://gerrit.chromium.org/gerrit/4442
Reviewed-by: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
diff --git a/server/cros/servotest.py b/server/cros/servotest.py
index 8597cbf..465dff3 100755
--- a/server/cros/servotest.py
+++ b/server/cros/servotest.py
@@ -17,10 +17,14 @@
     _ip = None
 
 
-    def initialize(self, host, servo_port, xml_config='servo.xml'):
+    def initialize(self, host, servo_port, xml_config='servo.xml',
+                   servo_vid=None, servo_pid=None, servo_serial=None):
         """Create a Servo object."""
         self.servo = autotest_lib.server.cros.servo.Servo(servo_port,
-                                                          xml_config)
+                                                          xml_config,
+                                                          servo_vid,
+                                                          servo_pid,
+                                                          servo_serial)
         self._ip = host.ip