t5500: show user name and host in diag-url

t5500: show user name and host in diag-url

The URL for ssh may have include a username before the hostname,
like ssh://user@host/repo.
When literal IPV6 addresses are used together with a username,
the substring "user@[::1]" must be converted into "user@::1".

Make that conversion visible for the user, and write userandhost
in the diagnostics

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>