Avoid including nova_virt_detect if nova_virt_type is set

There's no need for us to actually run through that entire
set of tasks if the value is specified already.

Change-Id: I6f3503fdfbe8fa43334da4360827078cd450ffcd

tasks/main.yml

@@ -70,6 +70,8 @@
     - always
 
 - include_tasks: nova_virt_detect.yml
+  when:
+    - nova_virt_type is not defined
   tags:
     - always
     - nova-config

tasks/nova_virt_detect.yml

@@ -17,14 +17,11 @@
   command: cat /proc/cpuinfo
   register: cpuinfo_contents
   changed_when: false
-  when:
-    - nova_virt_type is not defined
 
 - name: Register a fact for the nova kvm virt type
   set_fact:
     nova_virt_type: "kvm"
   when:
-    - nova_virt_type is not defined
     - cpuinfo_contents.stdout.find('vmx') != -1
       or cpuinfo_contents.stdout.find('svm') != -1
       or cpuinfo_contents.stdout.find('PowerNV') != -1