notify and gracefully skip credential-less testsa

tests/helper.rb

@@ -28,6 +28,14 @@ if ENV["FOG_MOCK"] == "true"
   Fog.mock!
 end
 
+# check to see which credentials are available and add others to the skipped tags list
+all_providers = ['aws', 'bluebox', 'brightbox', 'gogrid', 'google', 'linode', 'local', 'newservers', 'rackspace', 'slicehost', 'terremark']
+available_providers = Fog.providers.map {|provider| provider.to_s.downcase}
+for provider in (all_providers - available_providers)
+  Formatador.display_line("[yellow]Skipping tests for [bold]#{provider}[/] [yellow]due to lacking credentials (add some to '~/.fog' to run them)[/]")
+  Thread.current[:tags] << ('-' << provider)
+end
+
 # Boolean hax
 module Fog
   module Boolean