Passing the vms policy when launching an instance.

Fixes OS-113

VMS 2.6 introduces policies to handle the instance's memory instead
of setting a target limit. Each instance will use a policy of
$project_id.$flavor_name.$instance_name and vms can be configured
to set policies against this pattern.

Change-Id: Ibcf34f0498bdf2f347b2663a1acb191093d1b103
Merge "Passing the vms policy when launching an instance." into stable/essex