add guest support files for libvirt/unix schemes

add guest support files for libvirt/unix schemes

For systemd systems, the following files are used:
   - stapsh@.service.in: template file for a service which automatically
     respawns stapsh on a given virtio-serial port
   - 99-stapsh.rules: udev rules file that instantiates (or terminates)
     the stapsh service upon plugging in/out of virtio-serial ports

For SYSV systems, the following files are used:
   - stapsh-daemon.in: libexec script file that automatically respawns
     stapsh on a given virtio-serial port
   - stapshd.in: init script to control stapsh-daemon instances
   - 99-stapsh-init.rules: udev rules file that forces a configuration
     reload upon plugging in/out of virtio-serial ports
   - virtio_console.modules: ensures that the virtio_console module is
     loaded at boot time if virtio-serial ports are detected. This is a
     workaround for RHEL5, in which the module is not auto-loaded, but
     does no harm in other systems such as RHEL6.