skip MOE python test when MPI is not installed (microsoft#24116)

### Description
It is not common that dev machine have MPI installed. Skip the test if
MPI is not installed.

### Motivation and Context

Make it easy to run pytest in dev machine without the need to skip the
test manually.

Author: tianleiwu

onnxruntime/test/python/transformers/sharded_moe/test_sharded_moe.py

@@ -6,22 +6,28 @@
 import unittest
 
 import numpy as np
-from mpi4py import MPI
 from onnx import TensorProto, helper
 
 import onnxruntime
 
-np.random.seed(3)
+try:
+    from mpi4py import MPI
+
+    comm = MPI.COMM_WORLD
+except (ImportError, RuntimeError):
+    comm = None
 
-comm = MPI.COMM_WORLD
+has_mpi = comm is not None
+
+np.random.seed(3)
 
 
 def get_rank():
-    return comm.Get_rank()
+    return comm.Get_rank() if comm else 0
 
 
 def get_size():
-    return comm.Get_size()
+    return comm.Get_size() if comm else 0
 
 
 def print_out(*args):
@@ -254,7 +260,7 @@ def run_ort_with_parity_check(
     )
 
 
-def test_moe_with_tensor_parallelism(
+def run_moe_with_tensor_parallelism(
     hidden_size,
     inter_size,
     num_experts,
@@ -327,7 +333,7 @@ def get_fc2_tensor_shards(expert_weights):
     )
 
 
-def test_moe_with_expert_parallelism(
+def run_moe_with_expert_parallelism(
     hidden_size,
     inter_size,
     num_experts,
@@ -390,19 +396,22 @@ def test_moe_with_expert_parallelism(
 
 class TestMoE(unittest.TestCase):
     def test_moe_parallelism(self):
+        if not has_mpi:
+            self.skipTest("No MPI support")
+
         for hidden_size in [128, 1024]:
             for inter_size in [512, 2048]:
                 for num_experts in [64]:
                     for num_rows in [1024]:
                         print_out("EP")
-                        test_moe_with_expert_parallelism(
+                        run_moe_with_expert_parallelism(
                             hidden_size,
                             inter_size,
                             num_experts,
                             num_rows,
                         )
                         print_out("TP")
-                        test_moe_with_tensor_parallelism(
+                        run_moe_with_tensor_parallelism(
                             hidden_size,
                             inter_size,
                             num_experts,