tests: support default value in vagrant boxes.

tests/boxes.yml

@@ -1,70 +1,43 @@
 ---
 
-boxes:
+defaults:
+  uefi: true
+  ram: '6144'
+  cpu: '6'
 
+boxes:
   - name: arch-gnome
     box: aa-archlinux-gnome
     uefi: false
-    ram: '6144'
-    cpu: '6'
 
   - name: arch-kde
     box: aa-archlinux-kde
     uefi: false
-    ram: '6144'
-    cpu: '6'
 
   - name: arch-server
     box: aa-archlinux-server
     uefi: false
-    ram: '6144'
-    cpu: '6'
 
   - name: ubuntu-desktop
     box: aa-ubuntu-desktop
-    uefi: true
-    ram: '6144'
-    cpu: '6'
 
   - name: ubuntu-desktop24
     box: aa-ubuntu-desktop24
-    uefi: true
-    ram: '6144'
-    cpu: '6'
 
   - name: ubuntu-server
     box: aa-ubuntu-server
-    uefi: true
-    ram: '6144'
-    cpu: '6'
 
   - name: ubuntu-server24
     box: aa-ubuntu-server24
-    uefi: true
-    ram: '6144'
-    cpu: '6'
 
   - name: debian-server
     box: aa-debian-server
-    uefi: true
-    ram: '6144'
-    cpu: '6'
 
   - name: debian-gnome
     box: aa-debian-gnome
-    uefi: true
-    ram: '6144'
-    cpu: '6'
 
   - name: debian-kde
     box: aa-debian-kde
-    uefi: true
-    ram: '6144'
-    cpu: '6'
 
   - name: opensuse-kde
     box: aa-opensuse-kde
-    uefi: true
-    ram: '6144'
-    cpu: '6'
-