iotests: Fix test 104 under NBD

iotests: Fix test 104 under NBD

In the past, commit a231cb27 ("iotests: Fix 104 for NBD", v2.3.0)
added an additional filter to _filter_img_info to rewrite NBD URIs
into the expected output form.  This recently broke when we tweaked
tests to run in a per-format directory, which did not match the regex,
because _img_info itself is now already changing
SOCK_DIR=/tmp/tmpphjfbphd/raw-nbd-104 into
/tmp/tmpphjfbphd/IMGFMT-nbd-104 prior to _img_info_filter getting a
chance to further filter things.

While diagnosing the problem, I also noticed some filter lines
rendered completely useless by a typo when we switched from TCP to
Unix sockets for NBD (in shell, '\\+' is different from "\\+" (one
gives two backslash to the regex, matching the literal 2-byte sequence
<\+> after a single digit; the other gives one backslash to the regex,
as the metacharacter \+ to match one or more of <[0-9]>); since the
literal string <nbd://127.0.0.1:0\+> is not a valid URI, that regex
hasn't been matching anything for years so it is fine to just drop it
rather than fix the typo.

Fixes: f3923a72 ("iotests: Switch nbd tests to use Unix rather than TCP", v4.2.0)
Fixes: 5ba7db09 ("iotests: always use a unique sub-directory per test", v8.0.0)
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20230519150216.2599189-1-eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>