makebuildserver: use VB software virt if hardware is not available

This checks the local CPU settings to see if it has the right virtualizing
CPU instructions, and only uses VirtualBox hardware virtualization on
setups where it is available.  VMs instances usually do not provide these
instructions.  Where the CPU features are not available, it will use VB's
software virtualization.

makebuildserver

@@ -338,6 +338,20 @@ if type(config['baseboxurl']) in (list, tuple) or config['baseboxurl'][0] in ('(
 else:
     baseboxurl = '"{0}"'.format(config['baseboxurl'])
 
+# use VirtualBox software virtualization if hardware is not available,
+# like if this is being run in kvm or some other VM platform, like
+# http://jenkins.debian.net, the values are 'on' or 'off'
+hwvirtex = 'off'
+if sys.platform.startswith('darwin'):
+    # all < 10 year old Macs work, and OSX servers as VM host are very
+    # rare, but this could also be auto-detected if someone codes it
+    hwvirtex = 'on'
+elif os.path.exists('/proc/cpuinfo'):
+    with open('/proc/cpuinfo') as f:
+        contents = f.read()
+    if 'vmx' in contents or 'svm' in contents:
+        hwvirtex = 'on'
+
 # Generate an appropriate Vagrantfile for the buildserver, based on our
 # settings...
 vagrantfile = """
@@ -356,15 +370,17 @@ Vagrant.configure("2") do |config|
   config.vm.provider "virtualbox" do |v|
     v.customize ["modifyvm", :id, "--memory", "{2}"]
     v.customize ["modifyvm", :id, "--cpus", "{3}"]
+    v.customize ["modifyvm", :id, "--hwvirtex", "{4}"]
   end
 
-  config.vm.boot_timeout = {4}
+  config.vm.boot_timeout = {5}
 
   config.vm.provision :shell, :path => "fixpaths.sh"
 """.format(config['basebox'],
            baseboxurl,
            config['memory'],
            config.get('cpus', 1),
+           hwvirtex,
            config['boot_timeout'])
 if 'aptproxy' in config and config['aptproxy']:
     vagrantfile += """