test_driver: Implement virConnectGetAllDomainStats
test_driver: Implement virConnectGetAllDomainStats

Implement virConnectGetAllDomainStats in a modular way just like QEMU
driver, though remove some params in GetStatsWorker that we don't need
in test driver currently.

Only add the worker to get state so far, more worker will be added
in the future.

Signed-off-by: Luke Yue <52cb389a9dce6ad23a1ccbef87c68e8ebf30699c@gmail.com>
Reviewed-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

nertpinx/libvirt,jfehlig/libvirt,olafhering/libvirt,jfehlig/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,crobinso/libvirt,zippy2/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,zippy2/libvirt,olafhering/libvirt,crobinso/libvirt,crobinso/libvirt,nertpinx/libvirt,libvirt/libvirt,nertpinx/libvirt,zippy2/libvirt,nertpinx/libvirt,crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt