Fix type if instead of id

Change-Id: I59ef5a2f05d7f9b1fc82e84075e9e18c5e4d3491
diff --git a/src/com/mirantis/mcp/Common.groovy b/src/com/mirantis/mcp/Common.groovy
index e336d5a..00f8bfc 100644
--- a/src/com/mirantis/mcp/Common.groovy
+++ b/src/com/mirantis/mcp/Common.groovy
@@ -64,7 +64,7 @@
   def lbl = config.get('label', "buildpod.${env.JOB_NAME}.${env.BUILD_NUMBER}".replace('-', '_').replace('/', '_'))
   def toRun = config.get('function', 'none')
 
-  id (jnlpSlaveImg == 'none') {
+  if (jnlpSlaveImg == 'none') {
     error('jnlp Slave image MUST be defined')
   }