[CI/Build] Replace vllm.entrypoints.openai.api_server entrypoint with vllm serve command (#25967)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

.buildkite/nightly-benchmarks/scripts/launch-server.sh

@@ -181,18 +181,14 @@ launch_vllm_server() {
   if echo "$common_params" | jq -e 'has("fp8")' >/dev/null; then
     echo "Key 'fp8' exists in common params. Use neuralmagic fp8 model for convenience."
     model=$(echo "$common_params" | jq -r '.neuralmagic_quantized_model')
-    server_command="python3 \
-        -m vllm.entrypoints.openai.api_server \
+    server_command="vllm serve $model \
         -tp $tp \
-        --model $model \
         --port $port \
         $server_args"
   else
     echo "Key 'fp8' does not exist in common params."
-    server_command="python3 \
-        -m vllm.entrypoints.openai.api_server \
+    server_command="vllm serve $model \
         -tp $tp \
-        --model $model \
         --port $port \
         $server_args"
   fi

.buildkite/nightly-benchmarks/scripts/run-performance-benchmarks.sh

@@ -365,8 +365,7 @@ run_serving_tests() {
       continue
     fi
 
-    server_command="$server_envs python3 \
-      -m vllm.entrypoints.openai.api_server \
+    server_command="$server_envs vllm serve \
       $server_args"
 
     # run the server