Use ping option only for DCP WebSocket

* The Faye::WebSocket library will "buffer" some output of the connection and emit the `on :message` events in the order of the messages. However, when a ping is sent while the connection has already been closed, it will emit the `on :close` event immediately and drop all other messages (in that "buffer"). This is problematic for very short running executions that generate a long output (as this will be cut off without a proper exit message sent by Poseidon).

lib/runner/connection.rb

@@ -18,11 +18,7 @@ class Runner::Connection
 
   def initialize(url, strategy, event_loop, locale = I18n.locale)
     Rails.logger.debug { "#{Time.zone.now.getutc.inspect}: Opening connection to #{url}" }
-    # The `ping` value is measured in seconds and specifies how often a Ping frame should be sent.
-    # Internally, Faye::WebSocket uses EventMachine and the `ping` value is used to wake the EventMachine thread
-    # The `tls` option is used to customize the validation of TLS connections.
-    # Passing `nil` as a `root_cert_file` is okay and done so for the DockerContainerPool.
-    @socket = Faye::WebSocket::Client.new(url, [], strategy.class.websocket_header.merge(ping: 0.1))
+    @socket = Faye::WebSocket::Client.new(url, [], strategy.class.websocket_header)
     @strategy = strategy
     @status = :established
     @event_loop = event_loop

lib/runner/strategy/docker_container_pool.rb

@@ -129,7 +129,11 @@ class Runner::Strategy::DockerContainerPool < Runner::Strategy
   end
 
   def self.websocket_header
-    {}
+    # The `ping` value is measured in seconds and specifies how often a Ping frame should be sent.
+    # Internally, Faye::WebSocket uses EventMachine and the `ping` value is used to wake the EventMachine thread
+    {
+      ping: 0.1,
+    }
   end
 
   private

lib/runner/strategy/poseidon.rb

@@ -118,6 +118,8 @@ class Runner::Strategy::Poseidon < Runner::Strategy
   end
 
   def self.websocket_header
+    # The `tls` option is used to customize the validation of TLS connections.
+    # The `headers` option is used to pass the `Poseidon-Token` as part of the initial connection request.
     {
       tls: {root_cert_file: config[:ca_file]},
       headers: {'Poseidon-Token' => config[:token]},