Handle the case if not able to spin slave pod

This PR will handle the case if it is not able to spin a slave pod
Now it will through a nice message to user

Fixes openshiftio/openshift.io#3797

Author: piyush-garg

vars/pod.groovy

@@ -14,10 +14,18 @@ def call(Map args = [:], body = null) {
       ],
       volumes: volumes(),
     ) {
-      node (label) {
-        container(name: args.name, shell: args.shell) {
-            body()
+      try {
+        timeout(time: 30, unit: 'MINUTES') {
+          node (label) {
+            container(name: args.name, shell: args.shell) {
+              body()
+            }
+          }
         }
+      } catch (e) {
+        currentBuild.result = 'FAILED'
+        error "Not able to start a slave pod with label ${label}"
+        Events.emit(["build.end", "build.fail"], [status: status, namespace: namespace])
       }
     }
 }