Couple of changes and fixes:
  * $base_dir is now called $target_dir
  * Added $always_update and $auto_install boolean variables for dev boxes
  * Added $php_package_name due to different names of PHP package
  * For $auto_install a copy of composer.json is stored in /var/tmp and
    compared with current one so install is executed only when change is made.
    This is necessary because composer.json is in our case loaded from git.