seecoder-build-jenkins/config/set-executors.groovy

#!groovy
import groovy.json.JsonSlurper
import jenkins.model.*
import hudson.model.*

def parser = new JsonSlurper()
def config = parser.parseText(new File('/var/jenkins_home/config.json').text)

Jenkins.instance.setNumExecutors(config.num_executors)
println "--> set executors"