udevadm-verify: document '--resolve-names=late' and accept 'never' as is

udevadm-verify: document '--resolve-names=late' and accept 'never' as is

When '--resolve-names=late', systemd-udevd resolves user/group names
during each event being processed, and does not verify names on parse.
When '--resolve-names=never', systemd-udevd refuses any user/group names
on parse. Hence, the parser of udev rules behaves diffrently. Let's not
convert 'never' -> 'late' silently, and use the specified option as is.

This also updates man page and shell completion for --resolve-names
option.