Remove upstart support, use systemd-tmpfiles to create tmpfiles (Closes: #923032)

In this commit, the package gets aligned with Debian systemd policy:

1. Obsolete upstart support gets removed, it's not used by Ubuntu anyway

2. The systemd-tmpfiles from systemd package is used to create temporary files
   even when sysvinit-core is in use.   This means that phpX.Y-fpm now depends
   in systemd package.