Add extra info to log when MaxScale loads persisted configuration files

Since MaxScale 2.1 runtime config changes are saved and made persistent using 'internal' configuration files, on startup this is what you read:

2018-12-01 10:10:30 notice : Loading generated configuration files from '/var/lib/maxscale/maxscale.cnf.d'

2018-12-01 10:10:30 notice : Loading /var/lib/maxscale/maxscale.cnf.d/MariaDB-Monitor.cnf.

While the log message is formally correct it could help to be slightly more specific on what 'generated' there stands for and that variables defined in this generated files (derived from runtime config changes) may override variables in the default maxscale config file if the variables exist on both files. I say 'may' override since I don't know if it's impossible to have the case where a variable is only defined in the generated files.