AM-14 : [AM_CAT_01] The central catalog must be downloaded from : http:/www.exoplatform.com/addons/catalog
AM-8 [AM_CAT_06] When using --offline switch, only the local and cached catalog (if any) are used
--offline (and --no-cache AM-6) applies to add-ons local archives
Enforce to flush the message to display it before starting the process (which can be long and we want to know what is happening)