Convert SolidFire Capacity response to GiB

This patch fixes the reported free_capacity_gb response
in the SolidFire update_cluster_status method.

The initial patch fixed the free_capacity conversion,
however omitted the same fix that was needed for the
free_space calculation.

Closes Bug: #1284452

Change-Id: If034957764911ec92a6d7e603d0510325018db6d