Fixes Fedora 20 network issues when virtual

On Fedora 20 virtual machines biosdevname command
'Returns 4 if running in a virtual machine.'

This patch:
  - Uses the biosdevname command return value to detect if virtual
  - Uses /sys/net to get interface names - Might be better solution
  - Leaves unchanged the original 'bare metal' case - I wonder what for
    though?

Tested with Fedora Cloud image adapted for vagrant-libvirt

Fixes issue #4104

plugins/guests/fedora/cap/configure_networks.rb

@@ -14,7 +14,21 @@ module VagrantPlugins
         def self.configure_networks(machine, networks)
           network_scripts_dir = machine.guest.capability("network_scripts_dir")
 
+          virtual = false
           interface_names = Array.new
+          machine.communicate.sudo("/usr/sbin/biosdevname; echo $?") do |_, result|
+            virtual = true if result.chomp == '4'
+          end
+
+          if virtual
+            machine.communicate.sudo("ls /sys/class/net | grep -v lo") do |_, result|
+              interface_names = result.split("\n")
+            end
+
+            interface_names = networks.map do |network|
+               "eth#{network[:interface]}"
+            end
+          else
             machine.communicate.sudo("/usr/sbin/biosdevname -d | grep Kernel | cut -f2 -d: | sed -e 's/ //;'") do |_, result|
               interface_names = result.split("\n")
             end
@@ -35,6 +49,7 @@ module VagrantPlugins
                 interface_names.delete(interface_name)
               end
             end
+          end
 
           # Accumulate the configurations to add to the interfaces file as well
           # as what interfaces we're actually configuring since we use that later.