syslog: First step in retiring /etc/syslog.conf

This change does not affect the current usage of the module.  It does
allow manifests to choose to retire /etc/syslog.conf in favor or
fragments in /etc/rsyslog.d to control the syslog activity.  One
default fragment, 90-local.conf, that writes syslog messages
locally.

This change also include a fragment define that is used for the
management of rsyslog fragments.