gnocchi: remove useless keepalive adapter
gnocchi: remove useless keepalive adapter

This adapter is created by keystoneauth1 when no request session
object is pass to keystoneauth1. So remove it from Ceilometer.

Change-Id: I71f16ab0830cb4f3931be8615ffeb7fecf6f6af3

openstack/ceilometer,openstack/ceilometer