This removes the host-level cpu utilization metrics from nova-powervm.
Host-level cpu metrics are being cached at the pypowervm level where
running totals are kept for total cycles, firmware cycles, and user
cycles. The get_host_cpu_stats driver method converts these metrics
into the format expected by nova.
Change-Id: I85798a8baa81e6737674ec819e9f147a4374050d