Use activate instead of install for module activation

issue1456
review28931002

tests/scenario_sale_promotion.rst

@@ -7,7 +7,7 @@ Imports::
     >>> import datetime
     >>> from decimal import Decimal
     >>> from proteus import Model, Wizard
-    >>> from trytond.tests.tools import install_modules
+    >>> from trytond.tests.tools import activate_modules
     >>> from trytond.modules.company.tests.tools import create_company, \
     ...     get_company
     >>> from trytond.modules.account.tests.tools import create_chart, \
@@ -17,7 +17,7 @@ Imports::
 
 Install sale_promotion::
 
-    >>> config = install_modules('sale_promotion')
+    >>> config = activate_modules('sale_promotion')
 
 Create company::