(#9241) Add current_time request

Without this patch, no actual API calls are being made through the Fog
layer to the underlying rbvmobi later and ultimately to the vSphere
target API.

This patch adds a simple current_time request which is similar to a
"ping"  The layers and API are exercised fully using this simple API
call to retrieve the current time on the remote system.

This provides:

    >> Fog::Compute[:vsphere].current_time
    Tue Aug 30 20:46:27 UTC 2011
    >> Fog::Compute[:vsphere].requests
    [:current_time]

lib/fog/vsphere/compute.rb

@@ -8,6 +8,9 @@ module Fog
       recognizes :vsphere_port, :vsphere_path, :vsphere_ns
       recognizes :vsphere_rev, :vsphere_ssl, :vsphere_expected_pubkey_hash
 
+      request_path 'fog/vsphere/requests/compute'
+      request :current_time
+
       class Mock
 
         def initialize(options={})

lib/fog/vsphere/requests/compute/current_time.rb

@@ -0,0 +1,21 @@
+module Fog
+  module Compute
+    class Vsphere
+      class Real
+
+        def current_time
+          @connection.serviceInstance.CurrentTime
+        end
+
+      end
+
+      class Mock
+
+        def current_time
+          Time.now.utc
+        end
+
+      end
+    end
+  end
+end