[5.0] Workflow activity flow_stop doesn't change with False value

[Quentin THEURET @Amaris]

When we had a <field name="flow_stop">False</field> on a workflow, the set automatically the parameter flow_stop of the activity to True.

It's a big problem because if we do a mistake and set by error flow_stop to True, we should change the value on the database or with the client (Administration->Customization->Workflow Definitions->Activities).

For example with demo data:
    On sale module, I add <field name="flow_stop">True</field> to the activity 'wait_ship'. Aftert reload of the module, I change again with False value for the flow_stop.
    But, when I see the flow_stop value of 'wait_ship' activity on the Administration->Customization->Workflow Definitions->Activities menu, the value are always True.