Project Merge Request spinach test frequently failing.

We are now frequently getting a database locking issue when running the Project Merge Requests tests. This is the same failure as seen on this projects semaphore build: https://semaphoreapp.com/gitlabhq/gitlabhq/branches/master/builds/575

The previous scenario is still being loaded by poltergiest after the database has altered tables and truncated for the new scenario.

It looks to me to be related to 'I click Side-by-side Diff tab' which was changed in 3d2f1230