Fix #4746: support http or https for agent / server communication.

You need to edit site.cf and site.st to change the protocol:
       "inventory_upload_protocol"   string => "http";
   or
       "inventory_upload_protocol"   string => "https"
Merge pull request #389 from CedricCabessa/inventory_protocol_2.11

Fix #4746: support http or https for agent / server communication.