jenkins: reduce parallel, add verbose

V=s is openwrt, V=1 is here.
try and avoid weird problems with missing files like,
make[1]: *** No rule to make target '../../../include/libopencm3/stm32/g4/pwr.h', needed by 'rcc_common_all.o'.  Stop.

by turning down the paralellism a bit, it's a quad core arm, but it's
stil a little small machine.

tests/gadget-zero/Jenkinsfile

@@ -30,15 +30,15 @@ pipeline {
         		''' 
             }
         }
-    	stage('build') {
-    		steps {
-    		    sh '''
-    		    . .env3/bin/activate
-    		    make -j5 V=s
-    		    make -C tests/gadget-zero all V=s
-    		    '''
-    		}
-    	}
+        stage('build') {
+            steps {
+                sh '''
+                    . .env3/bin/activate
+                    make -j3 V=1
+                    make -C tests/gadget-zero all V=s
+                '''
+            }
+        }
         stage('Testprepare') {
             steps {
         		sh label: 'gadget0', script: '''