qemu.tests: update block mirroring/streaming cfg

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.tests: enhance drive_mirror class

if no event check, it sleep 3 seconds to wait job in steady status
really;

Signed-off-by: Xu Tian <xutian@redhat.com>
Merge pull request #971 from xutian/update_storage_migrate_cfg

qemu.tests: update block mirroring/streaming cfg