Enhancing Windows Tests on phpUnit

[hari-haran-ss]

Description:

• PR is to fix windows compatibility issues in running php-unit.
• The current repo works fine for mac, but not for windows.
• Handled the commands of scripts in composer json to a php file, as env variable setting is different for mac and windows. So, handled it generically to a php file (triggerTest.php).
• Similarly handled the system command execution based on OS for both win and mac /linux in runner.php.
• Fixed taskid conversion to int inside array pointer, as it passes string in windows.

[karanshah-browserstack]

Please raise a similar pr for selenium-3 branch too