tests: Use correct invalid TLD rather than localhost
tests: Use correct invalid TLD rather than localhost

RFC 6761 specifies an entire top-level domain which is guaranteed to
never resolve with a DNS query: invalid. Use that instead of localhost,
to eliminate the chance that the domain name we thought should never
resolve, actually resolves.

https://tools.ietf.org/html/rfc6761#section-6.4

This might fix bug #768282.

https://bugzilla.gnome.org/show_bug.cgi?id=768282

GNOME/libgdata,pwithnall/libgdata,pwithnall/libgdata