Previously people were not consistent about mocking which left internals in
a fragile state when running subfolder specs.
This introduces a simple helper `set_subfolder` which you can use to set
the subfolder for the spec. It takes care of proper configuration of subfolder
and teardown.
```
# usage
set_subfolder "/my_amazing_subfolder"
```
You should no longer stub base_uri or global_settings
e7cf4579a8