[FIX] point_of_sale: Closing a cash control session

Before the fix:
When creating a new session with Cash control POS then it was impossible to close the session.

After the fix:
The same flow as in 9.0 when closing a session

opw:691517

addons/point_of_sale/models/pos_session.py

@@ -230,6 +230,10 @@ class PosSession(models.Model):
             if not session.config_id.cash_control:
                 session.action_pos_session_close()
 
+    @api.multi
+    def action_pos_session_validate(self):
+        self.action_pos_session_close()
+
     @api.multi
     def action_pos_session_close(self):
         # Close CashBox

addons/point_of_sale/views/pos_session_view.xml

@@ -23,7 +23,7 @@
                     <button name="action_pos_session_closing_control" type="object" string="Validate Closing &amp; Post Entries"
                         attrs="{'invisible' : ['|', ('cash_control', '=', True),('state', '!=', 'opened')]}"
                         class="oe_highlight"/>
-                    <button name="action_pos_session_closing_control" type="object" string="Validate Closing &amp; Post Entries" states="closing_control"
+                    <button name="action_pos_session_validate" type="object" string="Validate Closing &amp; Post Entries" states="closing_control"
                         class="oe_highlight"/>
                     
                     <field name="state" widget="statusbar" statusbar_visible="opening_control,opened,closing_control,closed" nolabel="1" />