Add ability to prepend a string to config files

In cases where multiple applications are being deployed to the same
server, there's a good chance that naming collisions could apply when
copying the files to the configuration directory. If the user specifies
a "supervisord_configure_file_prefix", it will be prepended to every
filename that is generated.
Add support for a suffix on destination file

Rounds out the previous "prefix" functionality.
Merge pull request #1 from andrewbredow/prefixed-file-names

Add ability to prepend a string to config files