libvirt-test: Add test cases for nodedev-list

Test command: nodedev-list [--tree] [--cap <string>]

1) Run nodedev-list command and check return code.
2) If `cap_option == one`, results are also compared
   with devices get from sysfs.

Signed-off-by: Hao Liu <hliu@redhat.com>
libvirt: Fix nodedev_list in nodedev_create_destroy

1) Change nodedev_list according to change of API in virsh.py
2) We don't need to start VM when testing host node devices.

Signed-off-by: Hao Liu <hliu@redhat.com>