Provider does not need to set username

If the user sets this themselves, vagrant will pick it up. If the user
does not set it, vagrant will set a default. All this works without any
code on our end.

lib/vagrant-libvirt/action/read_ssh_info.rb

@@ -43,17 +43,12 @@ module VagrantPlugins
           ssh_info = {
             :host          => ip_address,
             :port          => machine.config.ssh.guest_port,
-            :username      => machine.config.ssh.username,
             :forward_agent => machine.config.ssh.forward_agent,
             :forward_x11   => machine.config.ssh.forward_x11,
           }
           
           ssh_info[:proxy_command] = "ssh '#{machine.provider_config.host}' -l '#{machine.provider_config.username}' nc %h %p" if machine.provider_config.connect_via_ssh
 
-          if not ssh_info[:username]
-            ssh_info[:username] = machine.config.ssh.default.username
-          end
-
           ssh_info
         end
       end