Prevent upstart export from deleting similarly named upstart files

The upstart export deletes files named ```#{app}*.conf``` which may include files other than the ones previously exported. For example, exporting with an application name of ```ab``` deletes ```abc.conf```. Here is a small fix to only delete ```#{app}.conf``` and ```#{app}-*.conf```, thus preserving files like ```application.conf```, ```application-process.conf```, etc.