virttest.utils_netperf: make the remote netperf path independent

This patch make the netperf path independent, the script will
re-geting the netperf package name when decompress the compressed
package.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
test.qemu.test: Refactor the code of netperf_udp

This patch refactor the code of netperf_udp using utils_netperf.
also make this test support windows guest.

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