powervm: make get_host_uptime output consistent with other virt drivers

The powervm driver was filtering out part of the uptime information so
that only system uptime was returned, not the number of users, load,
etc. The hypervisor API sample and the libvirt driver provide the full
uptime output, so this patch makes the powervm driver follow that
convention.

Fixes bug 1196630

Change-Id: I24134270cab9df97ff59c06e057406b4aa09992a
Merge "powervm: make get_host_uptime output consistent with other virt drivers"