config-tools: bugfix for saving configuration

When user delete all the VMs from UI, and click 'Save' button, a warning
message should appear to show that at least one VM is needed.

Tracked-On: #7532
Signed-off-by: Conghui <conghui.chen@intel.com>

misc/config_tools/configurator/packages/configurator/src/pages/Config.vue

@@ -349,6 +349,10 @@ export default {
       return errorFlag
     },
     saveScenario() {
+      if (_.isEmpty(this.scenario.vm)) {
+        alert("Please add at least one VM")
+        return
+      }
       let errorFlag = false
       errorFlag = this.confirmVmName()
       this.assignVMID()