testsuite may leave servers alive on error (#7549)
testsuite may leave servers alive on error (#7549)

in cases where you have
test name {
  start_server {
    start_server {
      assert
    }
  }
}

the exception will be thrown to the test proc, and the servers are
supposed to be killed on the way out. but it seems there was always a
bug of not cleaning the server stack, and recently (#7404) we started
relying on that stack in order to kill them, so with that bug sometimes
we would have tried to kill the same server twice, and leave one alive.

luckly, in most cases the pattern is:
start_server {
  test name {
  }
}
JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis