Jenkins script to bring slave online. The job would wait for 10 mins if the slave doesnt come online within that time it ll fail.

CheckSlaveOnline.groovy

import hudson.model.*
import hudson.AbortException;

def resolver = build.buildVariableResolver
// def node_names = resolver.resolve("NODE_LIST").split(",")
timeout_seconds = 600 // 10 mins 
sleepTime=30 // seconds

def node_name=resolver.resolve("NODE_NAME").replaceAll("\\s","")
slave = Hudson.instance.slaves.find({it.name == node_name});
if (slave != null) {
  computer = slave.getComputer();
  if (computer.isOffline()) {
    println "$node_name is offline.";
    computer.connect(true)
    long startTime = System.currentTimeMillis(); //fetch starting time
    while(computer.isOffline()||(System.currentTimeMillis()-startTime)<timeout_seconds*1000){
      println "$node_name still offline.";
      println "Sleep for $sleepTime seconds"
      sleep(sleepTime*1000)
    }
    if (computer.isOffline()) {
        throw new Exception('$node_name didnt come online. Kindly check')
    }
  }else {
    println "OK: $node_name is online";
  }
} else {
  println "Slave $node_name not found!";
}