[compute|Ecloud] Ecloud should not show up as a valid provider when not providing credentials

lib/fog/bin/ecloud.rb

@@ -1,6 +1,10 @@
 class Ecloud < Fog::Bin
   class << self
 
+    def available?
+      Fog::Ecloud::ECLOUD_OPTIONS.all? {|requirement| Fog.credentials.include?(requirement)}
+    end
+
     def class_for(key)
       case key
       when :compute

lib/fog/ecloud.rb

@@ -9,3 +9,9 @@ module Fog
 
   end
 end
+
+module Fog
+  module Ecloud
+    ECLOUD_OPTIONS = [:ecloud_authentication_method]
+  end
+end