recheck cache after acquired gnocchi_resource_lock
recheck cache after acquired gnocchi_resource_lock

Rechecking the cache after a sample got the gnocchi_resource_lock
because there is a possibility that the resource was already built
in cache by another ceilometer-collector.

This will reduce the unnecessay creation and update of resource in
gnocchi and improve the efficiency.

Change-Id: I85b30e770899c14ca06ae69b1f879106ceab0c5f
Closes-Bug:#1523193

idegtiarov/ceilometer,idegtiarov/ceilometer,ityaptin/ceilometer,openstack/ceilometer,ityaptin/ceilometer,openstack/ceilometer