* guix/scripts/substitute.scm (lookup-narinfos/diverse): New procedure.
(lookup-narinfo): Use it.
(process-query): Change #:cache-url to #:cache-urls.
[valid?]: Remove 'narinfo?' check, which is no longer necessary.
Use 'lookup-narinfos/diverse' instead of 'lookup-narinfos'.
(process-substitution): Change #:cache-url to #:cache-urls.
(%cache-url): Rename to...
(%cache-urls): ... this. Turn into a list.
(guix-substitute): Remove 'getaddrinfo' test with early exit. Adjust
calls to 'process-query' and 'process-substitution'.
* tests/substitute.scm: Change '%cache-url' to '%cache-urls'.
55b2fc1877