qemu.tests.mq_change_qnum: Support changing queues number during netperf and ping

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests: Redesign file_copy_stress.

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests: Update mq_change_qnum to match with our test case.

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests: Ping remote host after changing queues.

Signed-off-by: Feng Yang <fyang@redhat.com>
emu.tests.mq_change_qnum: Support setting negative queues number

add step log.

Signed-off-by: Feng Yang <fyang@redhat.com>