[dts] [PATCH V1] tests/vhost_pmd_xstats: add allow pci param to support tester and dut in same server and optimize code

[Tu, Lijuan]

> 1.Add -a option to support tester and dut in same server.
> 2.Use pmd.start_testpmd() to replace session.send_expect()
>   to start testpmd.
> 3.Move create dut ssh session from set_up to set_up_all
>   to reduce the number of creation.
> 4.Add close dut session in tear_down_all to close session
>   when suite execute over.

Applied