Generalize NoLeak Inspector for Fog::Service

Fog::Services can use the 'secrets' class method to list the symbols of
the instance variables not to display via #inspect.

lib/fog/aws/compute.rb

@@ -9,6 +9,8 @@ module Fog
       requires :aws_access_key_id, :aws_secret_access_key
       recognizes :endpoint, :region, :host, :path, :port, :scheme, :persistent, :aws_session_token, :use_iam_profile, :aws_credentials_expire_at
 
+      secrets    :aws_secret_access_key, :hmac, :aws_session_token
+
       model_path 'fog/aws/models/compute'
       model       :address
       collection  :addresses

lib/fog/aws/storage.rb

@@ -9,6 +9,8 @@ module Fog
       requires :aws_access_key_id, :aws_secret_access_key
       recognizes :endpoint, :region, :host, :path, :port, :scheme, :persistent, :use_iam_profile, :aws_session_token, :aws_credentials_expire_at
 
+      secrets    :aws_secret_access_key, :hmac
+
       model_path 'fog/aws/models/storage'
       collection  :directories
       model       :directory

lib/fog/core/service.rb

@@ -9,6 +9,12 @@ module Fog
     class Error < Fog::Errors::Error; end
     class NotFound < Fog::Errors::NotFound; end
 
+    module NoLeakInspector
+      def inspect
+        "#<#{self.class}:#{self.object_id} #{(self.instance_variables - service.secrets).map {|iv| [iv, self.instance_variable_get(iv).inspect].join('=')}.join(' ')}>"
+      end
+    end
+
     module Collections
 
       def collections
@@ -58,6 +64,7 @@ module Fog
           service::Mock.new(options)
         else
           service::Real.send(:include, service::Collections)
+          service::Real.send(:include, service::NoLeakInspector)
           service::Real.new(options)
         end
       end
@@ -163,6 +170,16 @@ module Fog
         @requests ||= []
       end
 
+      def secrets(*args)
+        if args.empty?
+          @secrets ||= []
+        else
+          args.inject(secrets) do |secrets, secret|
+            secrets << "@#{secret}".to_sym
+          end
+        end
+      end
+
       def requires(*args)
         requirements.concat(args)
       end

lib/fog/hp/compute.rb

@@ -8,6 +8,8 @@ module Fog
       requires    :hp_secret_key, :hp_account_id, :hp_tenant_id
       recognizes  :hp_auth_uri, :hp_servicenet, :persistent, :connection_options, :hp_use_upass_auth_style, :hp_auth_version, :hp_avl_zone
 
+      secrets     :hp_secret_key
+
       model_path 'fog/hp/models/compute'
       model       :address
       collection  :addresses