don't restore instance's state in plug_vifs

Instance's state should be restored in resume_state_on_host_boot
method, not in plug_vifs.
template: fix EzTemplate.create_instace arguments

This method now must take no arguments.
driver: get path to disk with VmHardDisk.get_image_path

get_sys_name may return some other data, so the only reliable
way to get path to directory with hard disk - using method
get_image_path.