Add support for reading installed lxc version from cli object

lib/vagrant-lxc/driver/cli.rb

@@ -23,6 +23,15 @@ module Vagrant
           run(:ls).split(/\s+/).uniq
         end
 
+        def version
+          if run(:version) =~ /lxc version:\s+(.+)\s*$/
+            $1.downcase
+          else
+            # TODO: Raise an user friendly error
+            raise 'Unable to parse lxc version!'
+          end
+        end
+
         def state
           if @name && run(:info, '--name', @name) =~ /^state:[^A-Z]+([A-Z]+)$/
             $1.downcase.to_sym

spec/unit/driver/cli_spec.rb

@@ -5,7 +5,6 @@ require 'vagrant-lxc/driver/cli'
 describe Vagrant::LXC::Driver::CLI do
   describe 'list' do
     let(:lxc_ls_out) { "dup-container\na-container dup-container" }
-    let(:exec_args)  { @exec_args }
     let(:result)     { @result }
 
     before do
@@ -24,6 +23,18 @@ describe Vagrant::LXC::Driver::CLI do
     end
   end
 
+  describe 'version' do
+    let(:lxc_version_out) { "lxc version:  0.x.y-rc1\n" }
+
+    before do
+      subject.stub(:run).with(:version).and_return(lxc_version_out)
+    end
+
+    it 'parses the version from the output' do
+      subject.version.should == '0.x.y-rc1'
+    end
+  end
+
   describe 'create' do
     let(:template)      { 'quantal-64' }
     let(:name)          { 'quantal-container' }