Corrected issue with /etc/init.d/supervisord script + some minor adjustments

Updated to last version available (3.1.3) …
    
    See https://pypi.python.org/simple/supervisor/

Corrected issue with "service supervisor restart" :
    
    => Failed to call refresh: Could not restart Service[supervisord]: Execution of '/etc/init.d/supervisord restart' returned 1: Restarting supervisord:
    
    Used last version of init script available from https://github.com/Supervisor/initscripts/blob/master/ubuntu
    Corrected supervisord path
    Removed use of supervisors.conf in init script

Permitted to give supervisor version as param (job was already half done)
Corrected comment because easy install is no more used