Before deleting the instance, check if the instance exists

The instance may not exist if there is a error before creating
instance or it failed to create, run the `cleanup` to delete the
non-existent instance will raise an error

Change-Id: I13e4b63be952967605093a4427f5b0ac4be280c3
Signed-off-by: dongwenjuan <dong.wenjuan@zte.com.cn>