nss: Fix tst-nss-files-hosts-long on single-stack hosts (bug 24816)

getent implicitly passes AI_ADDRCONFIG to getaddrinfo by default.
Use --no-addrconfig to suppress that, so that both IPv4 and IPv6
lookups succeed even if the address family is not supported by the
host.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>