Disable Monasca Log Metrics service by default

The Log Metrics service is an admin only service. We now have
support in Fluentd via the Prometheus plugin to create metrics
from logs. These metrics can be scraped into Monasca or Prometheus.
It therefore makes sense to deprecate this service, starting by
disabling it by default, and then removing it in the Xena release.
This should improve the stability of the Monasca metrics pipeline
by ensuring that all metrics pass via the Monasca API for
validation, and ensure that metrics generated from logs are
available to both Prometheus and Monasca users by default.

Change-Id: I704feb4434c1eece3eb00c19dc5f934fd4bc27b4