test_driver: Introduce testIOThreadInfo and generate IOThread infos

test_driver: Introduce testIOThreadInfo and generate IOThread infos

Introduce testIOThreadInfo to store IOThread infos: iothread_id,
poll_max_ns, poll_grow and poll_shrink for future usage.

Add an example of IOThread configuration to testdomfc4.xml, we also want
to generate default testIOThreadInfo for the IOThread configured in the
xml, so introduce testDomainGenerateIOThreadInfos, the values are taken
from QEMU.

Signed-off-by: Luke Yue <lukedyue@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>