provide more helpful error message than the one returned by the client, without context

builder/azure/arm/config.go

@@ -787,6 +787,10 @@ func assertRequiredParametersSet(c *Config, errs *packer.MultiError) {
 		for _, rid := range c.UserAssignedManagedIdentities {
 			r, err := client.ParseResourceID(rid)
 			if err != nil {
+				err := fmt.Errorf("Error parsing resource ID from `user_assigned_managed_identities`; please make sure"+
+					" that this value follows the full resource id format: "+
+					"/subscriptions/<SUBSCRIPTON_ID>/resourcegroups/<RESOURCE_GROUP>/providers/Microsoft.ManagedIdentity/userAssignedIdentities/<USER_ASSIGNED_IDENTITY_NAME>.\n"+
+					" Original error: %s", err)
 				errs = packer.MultiErrorAppend(errs, err)
 			} else {
 				if !strings.EqualFold(r.Provider, "Microsoft.ManagedIdentity") {