virttest.qemu: check_patch.py warning fix

************* Module virttest.qemu_vm
E0602:614:VM.make_create_command.add_cdrom: Undefined variable 'has_option'
E0602:614:VM.make_create_command.add_cdrom: Undefined variable 'help_text'
E0602:2060:VM.make_create_command: Undefined variable 'qemu_cmd'
E0602:2060:VM.make_create_command: Undefined variable 'help_text'

update add_smartcard and add_cdrom with new devices API.

Signed-off-by: Feng Yang <fyang@redhat.com>