Fix E2E tests for HFSDP + EP.

[cspades]

What does this PR do ?

• Clean logic for DP-Outer group retrieval between non-expert and expert groups. (Note that the inter-distributed-optimizer group is not dependent on EP size, so this PR should not change behavior.)
• Fix E2E unit tests using trivial DP and EP size.

Testing

• Tests are properly testing parallelisms now!

# Dense TP2 (DDP)
MLP(
  (linear_fc1): TELayerNormColumnParallelLinear(in_features=128, out_features=320, bias=False, TP=2)
  (linear_fc2): TERowParallelLinear(in_features=160, out_features=128, bias=False, TP=2)
)
...
  (local_experts): ModuleList(
    (0-3): 4 x MLP(
      (linear_fc1): TEColumnParallelLinear(in_features=128, out_features=640, bias=False, TP=1)
      (linear_fc2): TERowParallelLinear(in_features=320, out_features=128, bias=False, TP=1)
    )
  )

# Dense TP2 (MFSDP)
MLP(
  (linear_fc1): TELayerNormColumnParallelLinear(in_features=128, out_features=320, bias=False, TP=2)
  (linear_fc2): TERowParallelLinear(in_features=160, out_features=128, bias=False, TP=2)
)
...
  (local_experts): ModuleList(
    (0-3): 4 x MLP(
      (linear_fc1): TEColumnParallelLinear(in_features=128, out_features=640, bias=False, TP=1)
      (linear_fc2): TERowParallelLinear(in_features=320, out_features=128, bias=False, TP=1)
    )
  )

# EP2 ETP2 (MFSDP)
   (local_experts): ModuleList(
     (0-1): 2 x MLP(
       (linear_fc1): TEColumnParallelLinear(in_features=128, out_features=320, bias=False, TP=1)
       (linear_fc2): TERowParallelLinear(in_features=160, out_features=128, bias=False, TP=1)
     )
   )

# EP2 HFSDP2 (MFSDP)
  (local_experts): ModuleList(
    (0-1): 2 x MLP(
      (linear_fc1): TEColumnParallelLinear(in_features=128, out_features=640, bias=False, TP=1)
      (linear_fc2): TERowParallelLinear(in_features=320, out_features=128, bias=False, TP=1)
    )
  )

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