qemu.tests.sr_iov_hotplug_negative: Support hmp monitor and move driver unload to end of script.

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.tests.sr_iov_hotplug: Add enable_set_link to control use set_link command or not.

Need set enable_set_link to no when only VF/PF used ing guest.
As it do not suppot set_link command

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.cfg.sr-iov: Limit configure for rhel7 host.

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