
Nested KVM has many benefits, but when it doesn't work it fails jobs. This change defaults Ironic to using QEMU emulation, if someone wants their local devstack to autodetect, they should set IRONIC_VM_ENGINE="auto", or force KVM by setting IRONIC_KVM_ENGINE="kvm". Change-Id: I0367561ead972679250fc48d0f21b2c208e77e60