Squish: Stabilize tests using getEditorForFileSuffix()

This is especially useful when switching between files assigned to
the same type of editor. (e.g. cpp header <-> cpp source)

Change-Id: I0179e7086a6f25cb0ecc0b69da1f61adb21d8ac2
Reviewed-by: Robert Loehning <robert.loehning@digia.com>