allow bypassing executable setting

if you set executable to an empty string this avoids passing one to the command constructor
fixes #14813

lib/ansible/plugins/action/__init__.py

@@ -621,6 +621,7 @@ class ActionBase(with_metaclass(ABCMeta, object)):
         if self._connection.allow_executable:
             if executable is None:
                 executable = self._play_context.executable
+            if executable:
                 cmd = executable + ' -c ' + pipes.quote(cmd)
 
         display.debug("_low_level_execute_command(): executing: %s" % (cmd,))