This change adds three new role parameters `NovaCPUAllocationRatio`,
`NovaRAMAllocationRatio` and `NovaDiskAllocationRatio` for
configuring cpu_allocation_ratio, ram_allocation_ratio and
disk_allocation_ratio.
The default values for CPU and Disk allocation ratio are taken
as 0.0 as it will be updated by update_available_resource method
as mentioned in [1].
[1] https://specs.openstack.org/openstack/nova-specs/specs/stein/implemented/initial-allocation-ratios.html
Change-Id: Ia3c62668b0c1469e31aa8cd2c984b460eb06d970