BACKPORT - stable/icehouse - adjust default cpu and ram allocation ratios

As per support discussion, modify:

nova_cpu_allocation_ratio = 2.0
nova_ram_allocation_ratio = 1.0

Resolves issue: https://github.com/rcbops/ansible-lxc-rpc/pull/579
Cherry Pick from e16c0939ad0f1d6f9da3275f1c8ad5d5db211ab6