Fix test_that_user_can_select_run intermittent failure.

[test_that_user_can_select_run][test_link] is failing intermittently because the product version is not found in the drop-down menu when trying to create a new run.

The test creates a new product using the API to use for the run, after that it creates a new version for that product. When the test fails I noticed that the new version for the product is not created. Here is a link to the Jenkins [test run][run_link].

I could not reproduce the issue locally with manual testing, but the automated tests failed 30% of the time. It looks like the page changes too fast when trying to create the new version so I added a wait for the success message to be present.

[test_link]:https://github.com/mozilla/moztrap-tests/blob/master/tests/test_homepage.py#L70

[run_link]:http://selenium.qa.mtv2.mozilla.com:8080/view/All%20not%20B2G/job/moztrap.dev/647/HTML_Report/