Reworked the DaemonCommand.

* Accepts options for PID and log file.
* Uses posix_kill whenever available.
* Checks that the daemon actually started or stopped.
* Try to terminate then kill the daemon.
* Uses the logger or output instead of "echo".

Added a ProcessControl interface and implementations.

Closed #908

PHPCI/ProcessControl/ProcessControlInterface.php

@@ -0,0 +1,33 @@
+<?php
+/**
+ * PHPCI - Continuous Integration for PHP
+ *
+ * @copyright    Copyright 2015, Block 8 Limited.
+ * @license      https://github.com/Block8/PHPCI/blob/master/LICENSE.md
+ * @link         https://www.phptesting.org/
+ */
+
+namespace PHPCI\ProcessControl;
+
+/**
+ * A stateless service to check and kill system processes.
+ *
+ * @author Adirelle <adirelle@gmail.com>
+ */
+interface ProcessControlInterface
+{
+    /** Checks if a process exists.
+     *
+     * @param int $pid The process identifier.
+     *
+     * @return boolean true is the process is running, else false.
+     */
+    public function isRunning($pid);
+
+    /** Terminate a running process.
+     *
+     * @param int $pid The process identifier.
+     * @param bool $forcefully Whether to gently (false) or forcefully (true) terminate the process.
+     */
+    public function kill($pid, $forcefully = false);
+}