The `fault` should be included to log error message when vmware error happens

... because it can contain important information. For example:

(TaskInfo){
   key = "task-34928"
   task =
      (task){
         value = "task-34928"
         _type = "Task"
      }
   description =
      (LocalizableMessage){
         key = "com.vmware.vim.vpxd.vpx.vmprov.CreateDestinationVm"
         message = "Copying Virtual Machine configuration"
      }
   name = "CreateVM_Task"
   descriptionId = "Folder.createVm"
   entity =
      (entity){
         value = "group-v3"
         _type = "Folder"
      }
   entityName = "vm"
   state = "error"
   cancelled = False
   cancelable = False
   error =
      (LocalizedMethodFault){
         fault =
            (PlatformConfigFault){
               text = "Failed to attach port"
            }
         localizedMessage = "An error occurred during host configuration."
      }
   reason =
      (TaskReasonUser){
         userName = "root"
      }
   queueTime = 2014-09-10 12:46:48.283593
   startTime = 2014-09-10 12:46:48.290384
   completeTime = 2014-09-10 12:46:49.798797
   eventChainId = 157130
 }

Currently, only the localizedMessage is used to produce the log line in nova/virt/vmwareapi/driver.py _poll_task(). In this case, the message is too general. The important reason is said in the error.fault.text, so It should be reported as well.