Resolve subnet facts from secondary interfaces (#557)

BinaryLane edge hosts have a public primary IP, so region/environment/country/zone resolve to unknown even though their VPC NIC sits in a known subnet.

- match the primary IP first, unchanged for existing hosts
- otherwise scan interface bindings in name order, skipping lo, dum* and wg*
- add modules/libs/test/subnet_facts_check.rb (`ruby modules/libs/test/subnet_facts_check.rb`)

Reviewed-on: #557
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

modules/libs/test/subnet_facts_check.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+# ruby modules/libs/test/subnet_facts_check.rb
+module Facter
+  def self.value(_name)
+    {}
+  end
+
+  def self.add(*); end
+end
+load File.expand_path('../lib/facter/subnet_facts.rb', __dir__)
+
+iface = ->(*addresses) { { 'bindings' => addresses.map { |address| { 'address' => address } } } }
+
+checks = {
+  'primary ip wins over other interfaces' => [
+    { 'ip' => '198.18.17.5', 'interfaces' => { 'eth1' => iface.call('198.18.13.5') } }, 'drw1'
+  ],
+  'unmatched primary ip falls back to an interface' => [
+    { 'ip' => '203.0.113.5', 'interfaces' => { 'eth0' => iface.call('203.0.113.5'), 'eth1' => iface.call('198.18.24.11') } }, 'syd1'
+  ],
+  'lo, dum and wg interfaces are skipped' => [
+    { 'ip' => '203.0.113.5',
+      'interfaces' => { 'dum0' => iface.call('198.18.2.161'), 'lo' => iface.call('198.18.19.1'),
+                        'wg0' => iface.call('198.18.2.177') } }, 'unknown'
+  ],
+  'interfaces are scanned in name order' => [
+    { 'ip' => '203.0.113.5', 'interfaces' => { 'eth2' => iface.call('198.18.24.1'), 'eth1' => iface.call('198.18.17.1') } }, 'drw1'
+  ],
+  'missing ip and interfaces resolve to unknown' => [{}, 'unknown']
+}
+
+failures = checks.reject { |_name, (networking, expected)| SubnetAttributes.from_networking(networking)[:region] == expected }
+failures.each_key { |name| warn "FAIL: #{name}" }
+abort if failures.any?
+puts "ok (#{checks.size} checks)"