virt.test: fix some netperf issues

this patch:
1.fix the issue netperf cannot login with two nics,
2.add  netperf test support tcp_crr protocol
3.add an automated way to get the cdrom drive number.
4.modify the file path of netperf.tar.gz. now should
put the src file under "virt/shared/deps"
5.add more step info