[vcloud|compute] allow specifying a default VDC uri as 'vcloud_default_vdc'

This will default all operations to this VDC, rather
than requiring it to be specified in the model chain.

lib/fog/compute/models/vcloud/ips.rb

@@ -12,6 +12,7 @@ module Fog
         attribute :href
 
         def all
+          self.href = connection.default_vdc_href unless self.href
           check_href!( :messages => "Ips href of a Network you want to enumerate" )
           if data = connection.get_network_ips(href).body[:IpAddress]
             load(data)

lib/fog/compute/models/vcloud/networks.rb

@@ -13,6 +13,7 @@ module Fog
         attribute :href
 
         def all
+          self.href = connection.default_vdc_href unless self.href
           check_href!("Vdc")
           if data = connection.get_vdc(href).body[:AvailableNetworks][:Network]
             load(data)

lib/fog/compute/models/vcloud/servers.rb

@@ -13,6 +13,7 @@ module Fog
         attribute :href, :aliases => :Href
 
         def all
+          self.href = connection.default_vdc_href unless self.href
           check_href!(:parent => "Vdc")
           load(_vapps)
         end

lib/fog/compute/models/vcloud/tasks.rb

@@ -11,6 +11,7 @@ module Fog
         attribute :href, :aliases => :Href
 
         def all
+          self.href = connection.default_vdc_href unless self.href
           check_href!
           if data = connection.get_task_list(href).body[:Task]
             load(data)

lib/fog/compute/vcloud.rb

@@ -534,7 +534,7 @@ module Fog
       SCHEME = 'https'
 
       requires   :vcloud_username, :vcloud_password, :vcloud_host
-      recognizes :vcloud_port, :vcloud_scheme, :vcloud_path
+      recognizes :vcloud_port, :vcloud_scheme, :vcloud_path, :vcloud_default_vdc
       recognizes :provider # remove post deprecation
 
       model_path 'fog/compute/models/vcloud'
@@ -599,6 +599,10 @@ module Fog
           end
         end
 
+        def default_vdc_href
+          @vdc_href
+        end
+
         # login handles the auth, but we just need the Set-Cookie
         # header from that call.
         def do_login
@@ -754,6 +758,7 @@ module Fog
           @username = options[:vcloud_username]
           @password = options[:vcloud_password]
           @host     = options[:vcloud_host]
+          @vdc_href     = options[:vcloud_default_vdc]
           @path     = options[:vcloud_path]   || Fog::Vcloud::Compute::PATH
           @port     = options[:vcloud_port]   || Fog::Vcloud::Compute::PORT
           @scheme   = options[:vcloud_scheme] || Fog::Vcloud::Compute::SCHEME