Ensure nova_manage detects existing networks

Previously, there was a bug in the exists? method of
the nova_network provider where it could not detect
if a network already existed. This is b/c it
appended an extra /\d\d on the network id.

This commit corrects the logic so that existing
networks can be correctly detected.

lib/puppet/provider/nova_network/nova_manage.rb

@@ -6,7 +6,10 @@ Puppet::Type.type(:nova_network).provide(:nova_manage) do
 
   def exists?
     begin
-      nova_manage("network", "list").match(/^#{resource[:network]}\/[0-9]{1,2} /)
+      network_list = nova_manage("network", "list")
+      return network_list.split("\n")[1..-1].detect do |n|
+        n =~ /^(\S+)\s+(#{resource[:network]})/
+      end
     rescue
       return false
     end