Add set_user tools for test scenario

When changing the user of proteus, the context should be reloaded.

issue6652
review42551002

tests/scenario_analytic_purchase.rst

@@ -9,7 +9,7 @@ Imports::
     >>> from decimal import Decimal
     >>> from operator import attrgetter
     >>> from proteus import Model, Wizard, Report
-    >>> from trytond.tests.tools import activate_modules
+    >>> from trytond.tests.tools import activate_modules, set_user
     >>> from trytond.modules.company.tests.tools import create_company, \
     ...     get_company
     >>> from trytond.modules.account.tests.tools import create_fiscalyear, \
@@ -96,7 +96,7 @@ Create payment term::
 
 Purchase with analytic accounts::
 
-    >>> config.user = purchase_user.id
+    >>> set_user(purchase_user)
     >>> Purchase = Model.get('purchase.purchase')
     >>> purchase = Purchase()
     >>> purchase.party = supplier
@@ -133,7 +133,7 @@ Check invoice analytic accounts::
 
 Purchase with an empty analytic account::
 
-    >>> config.user = purchase_user.id
+    >>> set_user(purchase_user)
     >>> Purchase = Model.get('purchase.purchase')
     >>> purchase = Purchase()
     >>> purchase.party = supplier