Some tests had an orphaned host.

* This isn't normally a problem
* Except in mySQL 5.6, which is in use on one dev box just for access to EXPLAIN UPDATE, and which, unlike 5.5, won't allow an UPDATE of a NOT NULL field to NULL
* Yes, really. 5.5 allows this: https://gist.github.com/rgarner/9740859
Merge pull request #225 from alphagov/fix-tests-broken-in-mysql56

Some tests had an orphaned host