Add options for 3d acceleration (#1386)

When enabling video_accel3d, as graphics_gl is typically required, will 
by default set it to true unless explicitly set to false.

Enabling these should result in a significant performance improvement 
for any VM where the desktop is being used.

Fixes: #893
Fixes: #1009

spec/unit/templates/domain_all_settings.xml

@@ -112,9 +112,13 @@
 
     <input type='mouse' bus='ps2'/>
 
-      <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1' keymap='en-us'  />
+      <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1' keymap='en-us'  >
+        <gl enable='yes' />
+      </graphics>
       <video>
-        <model type='cirrus' vram='9216' heads='1'/>
+        <model type='cirrus' vram='9216' heads='1'>
+          <acceleration accel3d='yes'/>
+        </model>
       </video>
       <rng model='virtio'>
         <backend model='random'>/dev/random</backend>

spec/unit/templates/domain_spec.rb

@@ -112,6 +112,8 @@ describe 'templates/domain' do
       domain.shares = '1024'
       domain.cpuset = '1-4,^3,6'
       domain.nodeset = '1-4,^3,6'
+
+      domain.video_accel3d = true
     end
     let(:test_file) { 'domain_all_settings.xml' }
     it 'renders template' do