Adds RHEL-specific pathing

`supervisord` and `supervisorctl` are on different paths in RHEL and Debian systems.

The previous setting for path was not working:

    Exec {
      path => '/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin'
    }

Was getting this:

    Notice: /Stage[main]/Supervisord::Pip/Exec[install_setuptools]/returns: executed successfully
    default: Error: Could not find command '/usr/bin/easy_install'
    default: Error: /Stage[main]/Supervisord::Pip/Exec[install_pip]/returns: change from notrun to 0 failed: Could not find command '/usr/bin/easy_install'
    default: Notice: /Stage[main]/Supervisord::Pip/Exec[pip_provider_name_fix]: Dependency Exec[install_pip] has failures: true
    default: Warning: /Stage[main]/Supervisord::Pip/Exec[pip_provider_name_fix]: Skipping because of failed dependencies

Setting the exec path to contain `/usr/local/bin` fixes issue.

I also separated the paths into array format to make it easier to see easier path.

Related to https://github.com/puphpet/puphpet/issues/816