Fix uninitialized constant Riemann::Tools::VERSION (NameError)

When running the tools via bundler, `riemann/tools/version` is loaded
and `Riemann::Tools::VERSION` is defined.  But when running as a gem, it
is not loaded leading to an error at startup.

Explicitly require the version in the files that use it.

Author: smortex

lib/riemann/tools/apache_status.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'riemann/tools'
+require 'riemann/tools/version'
 
 # Collects Apache metrics and submits them to Riemann
 # More information can be found at http://httpd.apache.org/docs/2.4/mod/mod_status.html

lib/riemann/tools/cloudant.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'riemann/tools'
+require 'riemann/tools/version'
 
 # Gathers load balancer statistics from Cloudant.com (shared cluster) and submits them to Riemann.
 module Riemann

lib/riemann/tools/consul_health.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'riemann/tools'
+require 'riemann/tools/version'
 require 'socket'
 require 'net/http'
 require 'uri'

lib/riemann/tools/haproxy.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'riemann/tools'
+require 'riemann/tools/version'
 
 # Gathers haproxy CSV statistics and submits them to Riemann.
 module Riemann

lib/riemann/tools/http_check.rb

@@ -5,6 +5,7 @@
 require 'socket'
 
 require 'riemann/tools'
+require 'riemann/tools/version'
 
 # Test for HTTP requests
 module Riemann

lib/riemann/tools/nginx_status.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'riemann/tools'
+require 'riemann/tools/version'
 
 # Gathers nginx status stub statistics and submits them to Riemann.
 # See http://wiki.nginx.org/HttpStubStatusModule for configuring Nginx appropriately

tools/riemann-riak/lib/riemann/tools/riak.rb

@@ -2,6 +2,7 @@
 
 require 'English'
 require 'riemann/tools'
+require 'riemann/tools/version'
 
 # Forwards information on a Riak node to Riemann.
 module Riemann