If nova is installed on arm64 with active KVM, default to that.

There are problems using aarch64 booting UEFI with bare QEMU at the
moment, but if run under KVM it works well with a 4.15.0 kernel.

Tested with the current Ubuntu Bionic cloud image.  The Cirros 0.4.0
arm64 image has a 4.4.0 kernel which doesn't receive hardware
information from UEFI and panics when it cannot find an interrupt
controller, but without logging anything to console because it hasn't
detected the serial port either.

Change-Id: I7a39a03bf1bf959c650e4454bcb32f8c0c792619

tasks/nova_virt_detect.yml

@@ -18,6 +18,11 @@
   register: cpuinfo_contents
   changed_when: false
 
+- name: Check for existence of KVM node
+  stat:
+    path: "/dev/kvm"
+  register: dev_kvm
+
 - name: Register a fact for the nova kvm virt type
   set_fact:
     nova_virt_type: "kvm"
@@ -28,6 +33,8 @@
       or (cpuinfo_contents.stdout.find('pSeries') != -1
           and cpuinfo_contents.stdout.find('qemu') != -1
           and ansible_architecture == 'ppc64le')
+      or (dev_kvm.stat.ischr is defined and dev_kvm.stat.ischr
+          and ansible_architecture == 'aarch64')
 
 - name: Register a fact for the nova powervm virt type
   set_fact: