restapi: Fix size update in pools of ppc64 VMs

The size of VM pools could not be increased in ppc64 due to a problem
reading templates and inheriting properties from them. This patch fixes
this issue by correctly reading the VM template used in the pool and
using some of its properties as parameters.

Change-Id: I2c4a2a510cc96f6081f72af56ad84d6d54707677
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1148706
Signed-off-by: Vitor de Lima <vdelima@redhat.com>