Fix newrelic/mysql monitoring

Newrelic monitoring was not working properly because we were using the raxmon-agent db user which was created for 'localhost'. However the newrelic plugin for mysql was translating localhost to 127.0.0.1 and was getting a permission denied as raxmon-agent@127.0.0.1 were not existing.

In order to not rely on the cloud_monitoring user for newrelic I'm creating a new db user, it should not impact anything related to cloudmonitoring, it allows to fix the '127.0.0.1' and it allows to enable newrelic even if we don't have cloud_monitoring.