RD-3162 Drop _execute_system_workflow() (#3288)
RD-3162 Drop _execute_system_workflow() (#3288)

* Add system workflow code into prepare_executions

* Call prepare_executions instead of _execute_system_workflow

* Drop _execute_system_workflow completely
cloudify-cosmo/cloudify-manager,cloudify-cosmo/cloudify-manager,cloudify-cosmo/cloudify-manager