Write output from `sh' task action directly:

* Accept output as argument in Remote#execute;
* Modify ShellCommand so that env output is directly handled.

lib/producer/core/actions/shell_command.rb

@@ -3,7 +3,8 @@ module Producer
     module Actions
       class ShellCommand < Action
         def apply
-          output.puts remote.execute(arguments.first)
+          remote.execute(arguments.first, output)
+          output.puts
         end
       end
     end

lib/producer/core/remote.rb

@@ -23,8 +23,7 @@ module Producer
         @fs ||= Remote::FS.new(session.sftp.connect)
       end
 
-      def execute(command)
-        output = ''
+      def execute(command, output = '')
         channel = session.open_channel do |channel|
           channel.exec command do |ch, success|
             ch.on_data do |c, data|

lib/producer/core/testing/mock_remote.rb

@@ -6,18 +6,20 @@ module Producer
           raise 'no session for mock remote!'
         end
 
-        def execute(command)
+        def execute(command, output = '')
           tokens = command.split
           program = tokens.shift
 
           case program
           when 'echo'
-            tokens.join ' '
+            output << tokens.join(' ')
           when 'true'
-            ''
+            output << ''
           when 'false'
             raise RemoteCommandExecutionError
           end
+
+          output
         end
       end
     end