Add consistency check for service counts

zoe_master/preprocessing.py

@@ -46,6 +46,10 @@ def _digest_application_description(state: SQLManager, execution: Execution):
     for service_descr in execution.description['services']:
         essential_count = service_descr['essential_count']
         total_count = service_descr['total_count']
+        if essential_count > total_count:
+            execution.set_error()
+            execution.set_error_message('total_count is less than essential_count for service {}'.format(service_descr['name']))
+            return False
         elastic_count = total_count - essential_count
         counter = 0
         for service_n_ in range(essential_count):