Only run IPv6 tests if we have an IPv6 address

* test/src/process-tests.el (ipv6-is-available): New function for
checking whether we have a globally routable IPv6 prefix assigned.
(lookup-family-specification): Use 'ipv6-is-available' to check for
IPv6.  Use 'localhost' instead of 'google.com' to test
'network-lookup-address-info' API.
(lookup-google): Use 'ipv6-is-available' to check for
IPv6.

* test/lisp/net/nsm-tests.el (nsm-ipv6-is-available): Rename to
'ipv6-is-available', make identical to the one in
test/src/process-tests.el.
2 jobs for master in 46 minutes and 23 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #10029
test-filenotify-gio

00:32:47

passed #10030
test-gnustep

00:46:22

 
Name Stage Failure
failed
test-filenotify-gio Test

2 skipped results:
SKIPPED file-notify-test10-sufficient-resources
SKIPPED file-notify-test10-sufficient-resources-remote

make[1]: Leaving directory '/builds/emacs/emacs/test'
make: Leaving directory '/builds/emacs/emacs/test'
Cleaning up file based variables
ERROR: Job failed: exit code 1