MDL-48290 behat: Add log out after checking exported file

If the download step is the last in the scenario then we
can sometimes run into the situation where the download page
causes a http redirect but behat has already conducted its
reset (generating an error). By putting a logout step we avoid
behat doing the reset until we are off that page.

question/format/gift/tests/behat/import_export.feature

@@ -34,3 +34,8 @@ Feature: Test importing questions from GIFT format.
     And I set the field "id_format_gift" to "1"
     And I press "Export questions to file"
     And following "click here" should download between "1550" and "1650" bytes
+    # If the download step is the last in the scenario then we can sometimes run
+    # into the situation where the download page causes a http redirect but behat
+    # has already conducted its reset (generating an error). By putting a logout
+    # step we avoid behat doing the reset until we are off that page.
+    And I log out

question/format/xml/tests/behat/import_export.feature

@@ -36,6 +36,11 @@ Feature: Test importing questions from Moodle XML format.
     And I set the field "id_format_xml" to "1"
     And I press "Export questions to file"
     And following "click here" should download between "57000" and "58000" bytes
+    # If the download step is the last in the scenario then we can sometimes run
+    # into the situation where the download page causes a http redirect but behat
+    # has already conducted its reset (generating an error). By putting a logout
+    # step we avoid behat doing the reset until we are off that page.
+    And I log out
 
   @javascript @_file_upload
   Scenario: import some multiple choice questions from Moodle XML format