capability.rng: Guest features can be in any order.
nodedev.rng: Added <driver> element, <capability> phys_function and
virt_functions for PCI devices.
storagepool.rng: Owner or group ID can be -1.

schema tests: New capabilities and nodedev files; changed owner and
group to -1 in pool-dir.xml.
storage_conf: Print uid_t and gid_t as signed to storage pool XML.