test/reset: put unregister_worker after unregister_controllers.

From the log we can see that it reports ns_ctx was freed before it
was used. In unregister_controller, it still need ns_ctx to do io_complete.

And now this app works as a signle worker to do something.
Just need to change the order, execute unregister_worker after
unregister_controllers.

Fixes issue #1626

tested on clearlinux.

Signed-off-by: yidong0635 <dongx.yi@intel.com>
Change-Id: I392ff168abb862ba236a24b775fb31bb341e2157
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/4761


Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>