client: Ignore everything after first colon in userinfo

Use of the format "user:password" in the userinfo field is deprecated
and applications should not render as clear text any data after the
first colon as per rfc3986. Passwords have never been handled in
userinfo fields by GVfs, however, they are still part of the usernames,
which is wrong. Let's ignore such data in userinfo fileds.

https://bugzilla.gnome.org/show_bug.cgi?id=628430