Changes

#Suggestion received from a student: Create a virtual disk /dev/vda in centos2 in Lab 5 and use that virtual disk (vda) instead of /dev/sda (so use fdisk /dev/vda instead of using fdisk /dev/sda). This makes Lab 5 easier to handle accidental corruption students might make while doing that lab thereby destroying their centos2. This might require Lab 5 checker script to be tweaked to work with /dev/sda.