virt.tests: Updates to netperf

Get netperf src package from web;
Make the script compatible with netperf 2.6.0;
Modify the method of get winutils vol;
Modify the method of start netserver in windows guest
Using wait_for  to wait until all net perf clients start to work;
Reorganize the configure file.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>