jenkins auto cpu count (#30544)

* auto cpu

* build too

* need bash

Jenkinsfile

@@ -225,15 +225,17 @@ node {
         pcStage("PC tests") {
           // tests that our build system's dependencies are configured properly,
           // needs a machine with lots of cores
-          sh label: "test multi-threaded build", script: "scons --no-cache --random -j42"
+          sh label: "test multi-threaded build",
+             script: '''#!/bin/bash
+                        scons --no-cache --random -j$(nproc)'''
         }
       },
       'car tests': {
         pcStage("car tests") {
           sh label: "build", script: "selfdrive/manager/build.py"
           sh label: "test_models.py", script: "INTERNAL_SEG_CNT=250 INTERNAL_SEG_LIST=selfdrive/car/tests/test_models_segs.txt FILEREADER_CACHE=1 \
-              pytest -n42 --dist=loadscope selfdrive/car/tests/test_models.py"
-          sh label: "test_car_interfaces.py", script: "MAX_EXAMPLES=100 pytest -n42 --dist=load selfdrive/car/tests/test_car_interfaces.py"
+              pytest -n auto --dist=loadscope selfdrive/car/tests/test_models.py"
+          sh label: "test_car_interfaces.py", script: "MAX_EXAMPLES=100 pytest -n auto --dist=load selfdrive/car/tests/test_car_interfaces.py"
         }
       },