Use activate instead of install for module activation

issue1456
review28931002

tests/scenario_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 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_fiscalyear, \
@@ -20,7 +20,7 @@ Imports::
 
 Install purchase::
 
-    >>> config = install_modules('purchase')
+    >>> config = activate_modules('purchase')
 
 Create company::