Replace phpsh with "hhvmsh"

Creates a new /usr/local/bin/hhvmsh script that invokes HHVM in debug
mode attached to the local fcgi container. Provisioning and configuring
phpsh is moved to ::role::zend as phpsh does not work when /usr/bin/php
is a symlink to hhvm.

Bug: 67756
Change-Id: Iba5d6debd474b9cd7ec9ebde6512ac9b4fa03e40