Improve certificates test time

This will speedup the step ```And I do not see the upsell link on my dashboard```

Please verify from jenkins test report. Below is the result of latest build of master. 
https://jenkins.testeng.edx.org/job/edx-all-tests-auto-master/SHARD=2,TEST_SUITE=lms-acceptance/lastCompletedBuild/testReport/LMS/Verified%20certificates%20_%20Verified%20courses%20display%20correctly%20on%20dashboard/