Erroneous site state after something fails in a migration

[alberthajdu]

Something leaks from the migrations in case of an exception.

Repro:

1. Create a type from a migration.
2. In that migration after the type creation throw an exception.
3. In the dashboard you'll see under the "New" link that you can create that new type.
4. After a refresh it will no longer be there under the "New" link.

Here's my repro with 2 migrations and 2 types.

1. Before the migration there's only 1 type.
   

2. Right after the erronous migration there's 2 types.
   

3. After a refresh there's 1 type again.
   

This behavior could lead to a bigger issue.