Rename metering to Telemetry in user guide.
Rename metering to Telemetry in user guide.

Change-Id: Ib8f07733eca388a48d28efe5f4a3c6af13b5c825

openstack/openstack-manuals,Akasurde/openstack-manuals,kairoaraujo/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,gongysh2004/openstack-manual,potsmaster/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,saeki-masaki/openstack-manuals,potsmaster/openstack-manuals,gongysh2004/openstack-manual,openstack/openstack-manuals,openstack/openstack-manuals,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals