qemu.tests.multi_nic_stress: Make netperf link more configurable.

Current code always try to get netperf from shared/deps.

This patch make it more configurable. We can set multi netperf links,
web link, absolute path, relative path.

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests.netperf_udp: Make netperf link more configurable.

Current code always try to get netperf from link, but network may
not accessible in some pc.
As disscussed we can put netperf in shared/deps folder.

This patch make it more configurable. We can set multi netperf links,
web link, absolute path, relative path.

Signed-off-by: Feng Yang <fyang@redhat.com>
shared.deps: Add netperf tarball

Since it is necessary by default by the netperf test.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>