[Bugfix] fix sleepmode level2 e2e test (#4019)

### What this PR does / why we need it?

enable sleepmode level2 e2e test and add the check logic to ensure the
nz is not enabled.

### Does this PR introduce _any_ user-facing change?

no

### How was this patch tested?

use e2e tests


- vLLM version: v0.11.0
- vLLM main:
83f478bb19

Signed-off-by: wangx700 <wangxin700@huawei.com>

tests/e2e/multicard/test_external_launcher.py

@@ -108,6 +108,7 @@ def test_moe_external_launcher(model):
     assert proc.returncode == 0
 
 
+@patch.dict(os.environ, {"VLLM_ASCEND_ENABLE_NZ": "0"})
 def test_external_launcher_and_sleepmode():
     script = Path(
         __file__
@@ -154,6 +155,7 @@ def test_external_launcher_and_sleepmode():
     assert proc.returncode == 0
 
 
+@patch.dict(os.environ, {"VLLM_ASCEND_ENABLE_NZ": "0"})
 def test_external_launcher_and_sleepmode_level2():
     script = Path(
         __file__