[FEATURE] different priorityClass in driver and executor

[liujin1993]

When driver pod is preempted，whole sparkapplication will fail. So we want to set high priorityClass to all drivers，and low priorityClasses to executors

[ChenYi015]

@liujin1993 Thanks for raising this feature request. The priorityClass field of driver/executor pod has already been added by PR #2146. This issued can be closed then.

[ChenYi015]

Close this issue by #2146.