Send runner's hostname during registration

lib/config.rb

@@ -17,6 +17,12 @@ module GitlabCi
       end
     end
+    def hostname
+      @config.fetch('hostname') do
+        Socket.gethostname
+      end
+    end
+
     def token
       @config['token']
     end

lib/network.rb

@@ -75,7 +75,8 @@ module GitlabCi
     def register_runner(token)
       body = {
-        token: token
+        token: token,
+        hostname: config.hostname
       }
       opts = {