tools/download_manager.py: Clarify how to get out of the script

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest.qemu_vm: follow up with 'info block' changed in new qemu

add info block support of get_block() and
check_block_locked() in new qemu

Signed-of-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
qemu.tests.cdrom:add new qemu block format support in cdrom

add new qemu block format support in cdrom, like tray, lock,
block file, etc.

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>