Moved Thread/EventMachine creation inside of #run.

This cleans up the API a bit by removing the requirement of placing #run
inside a Thread.new {EventMachine.next_tick {}} block. That should not
be the caller's responsibility.

extensions/dns/api.rb

@@ -49,7 +49,7 @@ def self.pre_http_start(http_hook_server)
               end
             end
 
-            Thread.new { EventMachine.next_tick { dns.run(:upstream => servers, :listen => interfaces) } }
+            dns.run(:upstream => servers, :listen => interfaces)
 
             print_info "DNS Server: #{address}:#{port} (#{protocol})"
             print_more upstream_servers

extensions/dns/dns.rb

@@ -113,15 +113,19 @@ def remove_ruleset!
         # @option options [Array<Array>] :listen local interfaces to listen on
         def run(options = {})
           @lock.synchronize do
-            upstream = options[:upstream]
-            listen = options[:listen]
+            Thread.new do
+              EventMachine.next_tick do
+                upstream = options[:upstream] || nil
+                listen = options[:listen] || nil
+
+                if upstream
+                  resolver = RubyDNS::Resolver.new(upstream)
+                  @otherwise = Proc.new { |t| t.passthrough!(resolver) }
+                end
 
-            unless upstream.nil? || upstream.empty?
-              resolver = RubyDNS::Resolver.new(upstream)
-              @otherwise = Proc.new { |t| t.passthrough!(resolver) }
+                super(:listen => listen)
+              end
             end
-
-            super(:listen => listen)
           end
         end