Add riemann-tls-check to monitor TLS resources

Add a riemann-tls-check that accept a list of URI of resources to check
TLS certificates. For each URI, resolve the IP addresses that provide
the service, and for each IP address generate 6 events for:

1. availability: state (reachability + status of all the following
   metrics);
2. not after: state + metric (number of seconds until the certificate is
   expired);
3. not before: state + metric (number of seconds since the certificate
   is valid);
4. identity: state (certificate subject match the URI hostname);
5. trust: state (validity of the certificate trust chain);
6. OCSP satus: state (validity of the OCSP status if applicable).

A STARTTLS handshake is automatically done for imap://, ldap:// and
smtp://; a protocol specific handshake is done for mysql:// and
postgres:// URI.

bin/riemann-tls-check

@@ -0,0 +1,8 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+Process.setproctitle($PROGRAM_NAME)
+
+require 'riemann/tools/tls_check'
+
+Riemann::Tools::TLSCheck.run

lib/riemann/tools.rb

@@ -101,5 +101,13 @@ def run
     end
 
     def tick; end
+
+    def endpoint_name(address, port)
+      if address.ipv6?
+        "[#{address}]:#{port}"
+      else
+        "#{address}:#{port}"
+      end
+    end
   end
 end

lib/riemann/tools/http_check.rb

@@ -348,14 +348,6 @@ def redact_uri(uri)
         reported_uri.password = '**redacted**' if reported_uri.password
         reported_uri
       end
-
-      def endpoint_name(address, port)
-        if address.ipv6?
-          "[#{address}]:#{port}"
-        else
-          "#{address}:#{port}"
-        end
-      end
     end
   end
 end