Clear the main job description only at start of the job

Change-Id: Ia332da87893fc7c362898dd01689b36c6f4223ee
related-task: https://mirantis.jira.com/projects/PROD/issues/PROD-31616
diff --git a/src/com/mirantis/mk/Workflow.groovy b/src/com/mirantis/mk/Workflow.groovy
index e798a19..25191b7 100644
--- a/src/com/mirantis/mk/Workflow.groovy
+++ b/src/com/mirantis/mk/Workflow.groovy
@@ -94,7 +94,6 @@
  *                                If true: immediatelly fails the pipeline. DO NOT USE 'true' with runScenario().
  */
 def runSteps(steps, global_variables, failed_jobs, Boolean propagate = false) {
-    currentBuild.description = ''
     for (step in steps) {
         stage("Running job ${step['job']}") {
 
@@ -176,6 +175,8 @@
 
 def runScenario(scenario) {
 
+    // Clear description before adding new messages
+    currentBuild.description = ''
     // Collect the parameters for the jobs here
     global_variables = [:]
     // List of failed jobs to show at the end