work around device name problem with colocation (#329)

tensorpack/train/multigpu.py

@@ -131,10 +131,13 @@ class LeastLoadedDeviceSetter(object):
         self.ps_sizes = [0] * len(self.ps_devices)
 
     def __call__(self, op):
+        def sanitize_name(name):    # tensorflow/tensorflow#11484
+            return tf.DeviceSpec.from_string(name).to_string()
+
         if op.device:
             return op.device
         if op.type not in ['Variable', 'VariableV2']:
-            return self.worker_device
+            return sanitize_name(self.worker_device)
 
         device_index, _ = min(enumerate(
             self.ps_sizes), key=operator.itemgetter(1))
@@ -142,7 +145,7 @@ class LeastLoadedDeviceSetter(object):
         var_size = op.outputs[0].get_shape().num_elements()
         self.ps_sizes[device_index] += var_size
 
-        return device_name
+        return sanitize_name(device_name)
 
 
 class SyncMultiGPUTrainerParameterServer(MultiGPUTrainerBase, SingleCostFeedfreeTrainer):