libvirt-tests: Add test for libvirt_bench_domstate_switch_in_loop

Test for the performance of libvirt in domain state switching.

Steps:
    * start
    * reboot
    * shutdown (start for the latter operations)
    * suspend
    * resume
    * destroy

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>