The log format of xapi in the different XenServer versions

The function formatting the log messages of xapi in the different XenServer releases:

• for XS Cream: the make_log_message function found in log/debug.ml in the cream-bugfix branch of xen-api-libs.
• in XS Dundee, xapi has moved to the new Debug module in xcp-idl: https://github.com/xenserver/xen-api/commit/ab4a34fad5379381ec4e72375effd35413768ddd. From Dundee up to the newest development version of XS (Inverness), the format function, found in the lib directory of the xcp-idl repository is responsible for formatting log messages.